200g butter at room temperature, plus extra for the pan
250g light brown sugar
2 egg yolks
½ tsp vanilla extract
275g plain flour
1 tsp baking powder
150g chocolate chips
100g other cookie fillings, such as pretzels, chopped nuts, pieces of toffee or fudge, marshmallows vanilla ice cream, to serve (optional)
Heat oven to 180C/160C fan/gas 4. Tip the butter and sugar into a large mixing bowl, beat until combined, then stir in the yolks and vanilla. Tip in the flour, baking powder, chocolate chips, a pinch of sea salt and any other fillings you want to add. Mix until a crumbly dough forms.
Lightly butter a 25cm ovenproof frying pan. Spoon in and flatten the cookie mixture. For a gooey dessert, bake for 20 mins, leave to rest for 5 mins, then scoop straight from the pan and serve with ice cream, if you like. For a firmer cookie you can cut, bake for 30 mins, then leave to cool completely before cutting into wedges.