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, cornflour and cinnamon 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, all but a handful of the Christmas coloured M&Ms, and the chocolate chips 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 Christmas M&Ms into the top for decoration. 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
You can just use a bag of M&Ms and not bother dividing the colours – but I wanted this to look super Christmas like so I did. I used two of the larger M&M bags to get enough red/green/brown out of it. (I just ate the spare!)
You can of course use any other chocolatey treat you like in them, or even the dedicated Christmas M&M packets, or even the crispy or peanut M&Ms!
These delicious beings will last in an airtight container for up to 5 days, but honestly, they’ll be eaten before then.
Try microwaving them when they’ve cooled if you want a gooey cookie, or even add a scoop of ice cream!