Preheat your oven to 190ºc/170ºc fan and line a 9x9inch square tin with parchment paper, and leave to the side for now.
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 vanilla extract, and mix
Add the plain flour, cocoa powder, bicarbonate, salt and cornflour and mix to a cookie dough
Add in the dry Ingredients, and all but a small handful of M&Ms, and mix until a thick cookie dough is formed.
Press the mixture into the bottom of the tin and press in the handful of M&Ms into the top for decoration.
Bake the traybake in the oven for 18-20 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
I used oodles of Chocolate M&Ms in this recipe, and the colour on them stayed perfect even after baking, but I’m sure it would work with the Crunchy M&M’s, the Peanut M&M’s, or even smarties for example!
These delicious beings will last in an airtight container for up to 4-5 days, but honestly, they’ll be eaten before then.