Heat the oven to 350 degrees.

In the bowl of a stand mixer fitted with the paddle attachment, or in a bowl using a hand mixer, beat the butter and sugar until creamy, 3 to 4 minutes. Mix the flour and baking powder together and beat into the butter mixture.

Press the dough into the bottom of a 13- by 9-inch baking dish. Bake until golden, 30 to 35 minutes. Cool to room temperature.