Add the butter and sugar into the Thermomix and mix for 2 minutes/speed 4. Add the egg yolks and vanilla extract and mix for 30 seconds.
Add the flour and baking powder and mix for another 30 seconds till it's all combined.
Add the chocolate chips and marshmallows and mix on reverse for 30 seconds
If you were making regular cookies, you'd pop this batter into the fridge for about half an hour before you rolled it out, but since you're making giant cookies just spread it out into the bottom of two standard cake tins and smooth it out.
Pop in the oven for 20 - 25 mins.
Leave to cool, then decorate.
HINT: Mix a teaspoon of milk or water with two tablespoons icing sugar and spread it over the cooled cookie to help the icing from the icing pens stick to the cookie.
Recipe by Keeper of the Kitchen at https://www.keeperofthekitchen.com/2018/06/07/giant-cookies-fathers-day-occasions/