In a large bowl, cream the butter, granulated sugar, and brown sugar together until smooth and creamy. Add in the egg, almond extract (if using), and the vanilla extract, and mix to combine.
1/2 cup butter, 1/2 cup granulated sugar, 2 tbsp brown sugar, 1 large egg, 2 tsp vanilla extract, 1/4 tsp almond extract
Mix in the flour, baking powder, salt, and cornstarch just until the flour mixture barely disappears. Spread the batter into the prepared baking pan and bake in the preheated oven for 15 minutes. The center will still look raw but don't worry these bars will continue baking as they cool down.
1/2 tsp baking powder, 1 cup all purpose flour, 3 tbsp cornstarch, 1/4 tsp salt