*This post may contain affiliate links. Please see my disclosure for more details!*

Spooky and terrifyingly tasty halloween cookie bars with a black cookie dough, and stuffed with chocolate halloween M&Ms!


It’s October, it’s nearly Halloween… and I have been a bit poor on the Halloween scale so far this year. I’ve been so busy I have barely had the time, but I thought I would do something quick, easy and deliciously spooky for you guys to bake for the kids, or just because you’re craving cookies!

I have my pumpkin spice cookies, or even many halloween cakes such as my Halloween drip cake, or even my slime cupcakes.. but I know, there’s something about cookie bars that are just super easy and a go-to bake. 

Cookie Bars

This recipe is basically a copy of my M&M cookie bars because I just adore M&Ms, and they bake so well for cookies. Personally, I find that Smarties lose their colour quite a bit… and in general, I prefer M&Ms anyway. Are you the same?! Smarties or M&Ms? I feel like there is quite a divide on the internet about this!

Cookie bars are literally a recipe for cookie dough, just baked into a 9″ square tin instead of individual cookies. This makes it easier as you can just whack the mix into the tin, and portion how you like. 


I went to London to see Harry Potter and the Cursed Child recently, and if you go to Soho/Leicester Square quite often you’ll know that M&M world is there… and I couldn’t resist it. I bought all the themed chocolate sweets I could afford. That’s a bit of a lie, I just didn’t want to spend toooooo much as it would be a bit ridiculous.

When you go downstairs in M&M world, you basically find a GIANT pic’n’mix of M&Ms and it just looks amazing as well. All the colours perfectly separated, or themed ones dotted about… and I bought some Halloween ones just for these. They were mainly orange, a few yellow, and then some black/brown ones.

Of course, if you can’t go to an M&M world so casually, you will probably just have to pick out the colours from regular packets. It’s no bad thing, just eat the rest! 

Cookie Dough 

I thought, why not make the actual cookie black? Like to really contrast with the orange and yellow. I realise some people can get a bit funny about using food colouring, but when you use really good quality food colouring, it doesn’t matter even nearly as much because you use so little. I 100% recommend the Sugarflair Extra Black, as I just used half a teaspoon, and it made the bake completely black.

I haven’t personally ever coloured fondant black, as I usually just buy it, but for buttercreams, macarons etc, this Sugarflair Extra Black, is ideal. It really is insane. You can see from the pictures just how well it worked, and I am obsessed. The actual cookie bars don’t taste any different, they just taste deeeelightful and I am obsessed with cookie bars as you may know.


I personally bake these for 17/18 minutes because I like them to be quite gooey. The longer you bake, the dryer they will be. I’ve had people ask questions in the past about why their cookie bars are dry, and it literally is just overbaked.

If you use a different tin size, it can affect the bake, but keep an eye! These don’t really matter so much if they’re ‘underdone’ because they continue to bake when cooling! Enjoy!

Halloween Cookie Bars!

Spooky and terrifyingly tasty halloween cookie bars with a black cookie dough, and stuffed with chocolate halloween M&Ms!
Print Pin Rate
Category: Cookies
Type: Cookie Bars
Keyword: Halloween
Prep Time: 10 minutes
Cook Time: 18 minutes
Total Time: 28 minutes
Servings: 16 Cookies
Author: Jane's Patisserie


  • 115 g unsalted butter
  • 55 g granulated sugar
  • 135 g light brown sugar
  • 1/2 tsp Sugarflair Extra Black food colouring
  • 200 g plain flour
  • 50 g cocoa powder
  • 1 tsp bicarbonate of soda
  • 1/2 tsp salt
  • 1 tbsp cornflour
  • 1 medium egg
  • 1 tsp vanilla extract
  • 300 g Halloween M&Ms


  • Preheat your oven to 190C/170C Fan and line a 9x9inch square tin with parchment paper, and leave to the side for now.
  • In a large 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 black food colouring and whisk again. 
  • Add in the egg and the vanilla, and whisk again briefly until smooth.
  • Whisk/mix together the plain flour, cocoa powder, bicarbonate, salt and cornflour together so it's evenly distributed.
  • Add in the dry ingredients, the M&Ms (leave back a handful), and mix with a spatula until a thick cookie dough is formed.
  • Press the mixture into the bottom of the tin and press in the handful of into the top for decoration. Bake the traybake in the oven for 18-20 minutes, until the top of the cookie bake looks ‘dry’ and a skewer comes out basically clean, bar a few crumbs.
  • 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!


  • This delicious recipe is based on a recipe by Crunchy Creamy Sweet which I have adapted to grams, and swapped up slightly!
  • I used oodles of chocolate M&Ms in this recipe, which I bought from M&M World in London - which is how they are so easily colour specific!
  • You can buy themed M&Ms online, or pick colours out of packets, or try other Halloween chocolates like orange smarties (but M&Ms hold their colour better)
  • These delicious beings will last in an airtight container for up to 5 days, but honestly, they’ll be eaten before then.
  • If you want to bake these into cookies you can, but add in 50g more plain flour. They may still spread a smidge. 


Find my other Recipes on my Recipes Page!

You can find me on:

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.

This post may contain Affiliate Links.


  1. Holly on October 19, 2022 at 9:59 pm

    Hi! I’m looking to make these but have someone with an egg allergy, can the egg be substituted with anything else by any chance? Thank you!

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

      Hiya! Take a look at my began cookie recipe for egg substitutions in cookie bars! Hope this helps! x

  2. Holly on October 16, 2022 at 11:02 am

    Hi! I have someone with an egg allergy, is it possible to substitute the egg for something else in this recipe? Looking forward to making 🙂 x

    • Jane's Patisserie on October 21, 2022 at 10:34 am

      Hiya! Have a look at my vegan cookies for egg substitutes in vegan cookie bars! Hope this helps! x

  3. anna on October 27, 2021 at 3:49 pm

    5 stars
    Hiya, me and my friend made these for our class last week. They were so good! We used smarties instead of M&Ms and it still worked perfectly. Thanks for sharing! 🙂

  4. Tillie/Lily on October 30, 2020 at 9:47 am

    5 stars
    Hi Jane

    Thank you so much for replying i do not think we used the same tray as you. Me and my friend Lily were inspired by your blog to do our own cooking/baking club and now we are making the pumpkin spice frappe cake for Halloween. Thanks for all your amazing recipes i’m actually having your s’mores cake for my birthday cake because i love s’mores so much.

    Thanks Jane

  5. Tillie/lily on September 27, 2020 at 3:59 pm

    4 stars
    Me and my friend made these cookies we love Halloween and cant celebrate it this year because of the virus . We wanted 24 and we only got 10 we are very disappointed cause if we were to cut them to 24 they would be very very small they look good just not enough we also had to add milk and an egg as the mix was very dry but they taste great.

    • Jane's Patisserie on September 27, 2020 at 4:37 pm

      Hey! If you baked it into the same size tray, and followed the recipe, you would get however many pieces you cut it into. I use a 9″ square as listed, and cut it into 16 pieces.. if you did follow the recipe, you will have just made the portions bigger (which they would be if you cut them into 10)..

Leave a Comment

Recipe Rating

This site uses Akismet to reduce spam. Learn how your comment data is processed.