Preheat oven to 350℉. Coat a 9×9 inch pan with nonstick spray. Set aside.
Place butter into a microwavable bowl and melt. Stir in 3/4 cup white chocolate chips until smooth.
In a separate mixing bowl, add sugar, brown sugar, flour, baking powder, salt and 1/2 cup white chocolate chips, stir in melted butter mixture.
Add eggs, half and half and vanilla extract and combine thoroughly. Pour batter into prepared baking dish. Top with cut up pieces of Kit Kat bars.
Bake for 30-35 minutes or until cooked through. Cool then cut into squares.