Preheat the oven to 180°C fan / 200°C conventional, and line a dark baking tray with baking paper.
Cream the softened butter until smooth.
125 grams Salted butter
Beat in the light brown sugar and caster sugar until well combined.
75 grams White caster sugar, 120 grams Light brown sugar
Mix in the egg and vanilla extract.
1.5 teaspoons Vanilla extract, 1 medium Egg
Fold in the self-raising flour and cornflour until a soft cookie dough forms.
225 grams Self-raising flour, 2 teaspoons Cornflour
Fold through the chocolate chips, saving a small handful for decorating later.
150-200 grams Chocolate Chips
Scoop heaped tablespoons of dough (roughly golf ball sized) and roll into balls that are slightly taller than they are wide.
Place around 6 cookie dough balls onto the prepared baking tray, leaving space between each one. You'll need to bake the cookies in batches.
Bake for 10 minutes. The cookies should look pale golden around the edge but still a little underbaked in the middle.
Remove from the oven and immediately firmly bang the tray on the worktop a few times (this will give the cookies that crinkly rippled top). Use a large cookie cutter to gently shape each cookie into a neat circle, then press the reserved chocolate chips into the tops. Sprinkle a pinch of sea salt flakes over each cookie.
Leave the cookies to cool on the tray for 10 minutes before serving. They'll continue to firm up while staying perfectly soft and chewy in the middle.