Combine the melted butter, brown sugar, and granulated sugar
Mix in the egg and vanilla
Gently fold in the flour, cornstarch, baking soda, salt, and baking powder
Stir in the chocolate chips
Combine softened butter, cocoa powder, flour, sugar, vanilla, and milk in a bowl
Mix until smooth with no lumps
Preheat the oven to 350°F
Roll the dough into balls (approximately 80g each) and flatten slightly
Add the brownie filling to the center of each cookie
Seal completely with dough
Bake for 12-14 minutes
