Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.

Cream together 250 grams of unsalted butter, 200 grams of granulated sugar, and 120 grams of brown sugar until light and fluffy.

Add one whole egg, one egg yolk, and one teaspoon of vanilla extract and mix until combined.

Whisk together 200 grams of flour, 80 grams of cocoa powder, one teaspoon of kosher salt, and the baking powder and soda.

Gradually mix the dry ingredients into the wet mixture until just combined.

Fold in 300 grams of Kit Kat bars and 150 grams of chopped chocolate.

Scoop generous spoonfuls of dough onto the prepared baking sheet, spaced about 2 inches apart, and bake for 12-15 minutes.

Let cool on the baking sheet for 5 minutes before transferring to a wire rack.