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 till smooth. (I used an electric whisk)
Add in the Dry Ingredients, and mix till 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!
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!