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 (if you are using) 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 the chocolate chips and mix with a spatula until a thick cookie dough is formed.
Finally, add in the chocolates! I don't chop mine up. Fold through the mixture as best you can!
Press the mixture into the bottom of the tin and bake the traybake in the oven for 18-22 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 Celebrations as I bought SO many. I used all of them, as I'm not fussy when it comes to Celebrations.. but use your favourites if they're for you! Or even use up the ones you don't like and give them away!
You can easily use others such as Heroes, Roses, Quality street and so on - however, if you are using a lot of soft centre ones, I would recommend freezing them first.
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!