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Gooey chocolate chip cookie, gooey vanilla marshmallow, make THE most delicious s’mores cookie bars ever!

Ohhh so like.. yeah. Cookie bars happened again! I honestly couldn’t resist. I’ve actually baked these beauties several times, getting them slightly more perfect each time. I tried these in quite a few different ways, and honestly, this one stuck.

S’mores

How could you not love marshmallow and cookies together?! If you like s’mores then you will love these. Honestly… biscuit, marshmallow, and chocolate together is heaven. You can also try these guys warmed a little for ultimate s’mores experience.

My s’mores dip is slightly out of this world in my opinion, and I recently made my no-bake s’mores cheesecake again, along with my s’mores cake for a party and everyone said how good a cookie version would be… so I knew I should finally post this recipe.

So imagine a gooey, chocolatey cookie together with gooey marshmallow; my idea of heaven! These would suit being more towards Halloween and bonfire night, but I just couldn’t resist posting them now – it’s like marrying two of my favourite things together, s’mores and cookies. 

Cookie bars

I went for my usual cookie bar style recipe, as I have also used in my Mini Egg cookie bars and Rolo cookie bars. These recipes are just utterly delicious, and since discovering what cookie bars all those years ago, I have been obsessed and more obsessed as time has gone on. 

  • Butter – you can use either a baking spread, or an unsalted block butter at room temperature – both work well 
  • Sugars – I classically use a mixture of white granulated sugar and light brown soft sugar because I like the flavour balance from both of them
  • Egg – I only ever use one egg, and I always buy medium, but one large would also work 
  • Flavours – I love the addition of vanilla but this is optional
  • Flours – I use plain flour, as always, but I also add in some cornflour for texture 
  • Raising agent – you only want to use bicarbonate of soda in these, which is nearly always needed in my cookie recipes 
  • Salt – optional, but I adore a chunky sea salt added in for the balance of sweetness 
  • Chocolate – you can use any you want, but I typically use milk or dark chocolate, or a mixture of both 

Marshmallow

It’s hard to explain sometimes, but the marshmallow fluff makes the cookies gooier, and stops them drying out and just makes them utterly glorious. When I first wrote this recipe, and still often now if I am pressed for time, I use a shop bought marshmallow fluff because it’s just SO easy to use. It’s about 200g in the tub, and I slightly microwave the tub to soften the marshmallow and then scrape it out of the tub onto the cookie dough. 

If you have a look at my s’mores cookie recipe however, you can see that I made my own version of marshmallow fluff for this, and it will work perfectly for these cookie bars as well – it’s a bit more intense to make your own, but it’s worth it if you are up for it. 

Assembly

I love anything s’mores as I have said, but these are just DELIGHTFUL. You need to split the cookie dough into two sections… two thirds and one third.It can be a little bit faffy, but you need to press down the first lot of cookie dough so its even (often easier to use your hands) and then spread the marshmallow fluff on top.

The problem is, marshmallow fluff is so sticky, it’s easier to microwave it for 20 seconds so it’s spreadable! Then comes the problem of putting the next third of cookie dough on. I tend to pick the last third of cookie dough into small little pieces and then place it all over the top of the marshmallow so it spreads. You won’t be able to dollop it all on and spread with a spatula as it will just move all of the marshmallow out of the way. 

Tips & Tricks 

You can use any chocolate in the cookie bars, I just thought milk or dark chocolate would be a great fit for this recipe! I wouldn’t recommend using actual marshmallows for these though as they will just boil and disappear – nobody wants to look forward to these and them see no marshmallow goodness as the end of it – but you can make your own marshmallow fluff from my s’mores cookie recipe. 

  • These cookie bars will last for 4-5+ days at room temperature 
  • You can freeze these cookie bars for 3+ months
  • I use this 9×9″ square tin for this recipe

S'mores Cookie Bars

Gooey chocolate chip cookie, gooey vanilla marshmallow, make THE most delicious s'mores cookie bars ever!
Print Pin Rate
Category: Dessert
Type: Cookie Bars
Prep Time: 10 minutes
Cook Time: 20 minutes
Total Time: 30 minutes
Servings: 16 Pieces
Author: Jane's Patisserie

Ingredients

  • 275 g plain flour
  • 1 tsp bicarbonate of soda
  • 1/2 tsp salt
  • 1 tbsp cornflour
  • 115 g unsalted butter
  • 100 g granulated sugar
  • 100 g light brown sugar
  • 1 medium egg
  • 1/2 tsp Vanilla Extract
  • 300 g milk/dark chocolate
  • 1x tub marshmallow fluff

Instructions

  • Preheat your oven to 190C/170C Fan and line a 9x9inch square tin with parchment paper, and leave to the side for now.
  • Whisk/Mix the plain flour, bicarbonate, salt and cornflour together so its evenly distributed – leave to the side.
  • In a larger bowl, melt the butter. Add in the two sugars, and whisk for about 2 minutes so the sugar starts to dissolve and the mixture is smooth. Add in the egg and the vanilla, and whisk again briefly until smooth. (I used an electric whisk)
  • Add in the dry Ingredients, and mix until a cookie dough is formed. Add in the chocolate chips and mix with a spatula until they’re spread through the cookie dough evenly.
  • Press two thirds of the the mixture into the bottom of the tin. Microwave the marshmallow fluff for 20-30 seconds and spread over the cookie dough.
  • Spread/cover the marshmallow fluff layer in the other third of the cookie dough. It might be hard to spread it, so I rolled it out onto some cling film, and then turned it onto the marshmallow layer to make it even. Bake the traybake in the oven for 20-25 minutes, until the top of the cookie bake looks ‘dry’!
  • Leave the cookie bake to cool for about 10 minutes, then leave to cool fully on a wire rack. Cut the bake into 4×4 for decent sizes, or 5×5 for smaller ones! Enjoy!

Notes

  • If you try to use actual marshmallows, they will boil and basically disappear into the cookie bars. Marshmallow fluff is usually found in the supermarkets near the Nutellas and jams etc, and its quite commonly available!
  • These delicious beings will last in an airtight container for up to 4 days, but honestly, they’ll be eaten before then.
  • You can use whatever chocolate you want in the middle – but I used dark chocolate chips. Milk or white work well, or even a flavoured chocolate!
  • Try microwaving them when they’ve cooled if you want a gooey cookie, or even add a scoop of ice cream!
  • This post was not inspired by anyone in particular – but I took inspiration from photos on Pinterest/Instagram and just has a go at it!

Find my other recipes on my Recipes Page!

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J x

© Jane’s Patisserie. All images & content are copyright protected. Do not use my images without prior permission. If you want to republish this recipe, please re-write the recipe in your own words and credit me, or link back to this post for the recipe.

53 Comments

  1. Poppy lawn on March 20, 2026 at 10:42 am

    Thank you so much I am making these for my cousins 18th birthday

  2. Dan on February 14, 2026 at 4:20 pm

    4 stars
    Not sure what I did wrong but after 15 mins cooling in the tin I took them out and they collapsed! They looked cooked (the cookie dough on top had browned). Still taste delicious but I wasn’t able to slice them!

    • Jane's Patisserie on February 15, 2026 at 9:07 am

      This sounds like they were underbaked slightly – your oven might just need a little longer (or if you use a different shaped/sized tin, this can cause it)



  3. Jemma on September 7, 2024 at 8:59 pm

    Trying this soon for a Macmillan coffee morning. Is the sugar used actual granulated sugar or is it caster sugar? Thank you.

  4. Hazel on December 7, 2023 at 10:15 pm

    Could I make the cookie dough in advance and freeze it and then make them up with the fluff and bake them at a later date? Would like to make these for over Christmas
    and I’m trying to think how much prep I can get done in advance!

  5. Christine on October 24, 2023 at 9:49 am

    Can these be frozen. I know cookie freeze well but unsure of the fluff. Thanks

  6. Jane on May 6, 2023 at 4:05 pm

    Tried this recipe just now.. Looks lovely
    I used peanut butter chips
    Thank you Jane x

  7. Nicola on January 18, 2023 at 8:27 pm

    Hey Jane,

    Reckon if you freeze mini marshmallows before putting it into the mixture, it’ll stop it from melting?

    • Jane's Patisserie on January 30, 2023 at 11:19 am

      Hiya! Sadly I don’t think so, though it is always worth a try! Enjoy! x



  8. Beth on October 20, 2022 at 11:51 am

    3 stars
    I followed the recipe to a t and ended up with a really liquid-y dough. I had to add more flour to do anything with it and ended up with more of a dry cake than a cookie. Really disappointed.

    • Jane's Patisserie on October 21, 2022 at 10:56 am

      Hiya! Unfortunately I think something may have been measured incorrectly – I have never experienced this with a cookie bar recipe! So sorry this happened! x



  9. Claire S on October 19, 2022 at 11:05 am

    Hi Jane these look incredible!! Would it work to put a layer on just marshmallows in the middle, I have tons in the cupboard?

    • Jane's Patisserie on October 21, 2022 at 10:53 am

      Hiya! Sadly I don’t think this would work – they tend to dissolve into basically nothing! Hope this helps! x



  10. Sam Williams on October 12, 2022 at 2:36 pm

    I have tried getting the fluff in every supermarket but cannot find any anywhere are you able to advise me which store you found sone please thanks

    • Jane's Patisserie on October 13, 2022 at 3:26 pm

      Hiya! I usually just order on Amazon, hope this helps! x



    • Aimee on October 21, 2022 at 9:20 am

      I found it in sainsburys on an end isle….where a their American sweets are…hope that helps



  11. Helen on September 10, 2022 at 5:27 pm

    5 stars
    Amazing recipe, my boyfriend asks me almost on a daily basis when I’m next making them so I’ve stocked up on marshmallow fluff for the foreseeable! They are absolutely delightful!

  12. olivia on February 27, 2022 at 11:47 am

    also, how would i adjust the baking time for using a 7×7 tin instead?

  13. olivia on February 27, 2022 at 11:39 am

    hiya jane! does the marshmallow fluff need to be microwaved? as these look relish and i’d love to make them, however do not own a microwave x

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