Preheat oven to 350°F. Grease and flour a 9×13 inch baking pan.

In a bowl, combine flour, baking powder, and salt; set aside.

In the same bowl, cream butter and sugar until light and fluffy. Add egg and beat until just blended. Stir in vanilla extract; set aside.

Add dry ingredients to wet ingredients; mix until just combined. Pour batter into prepared pan; spread evenly with a spoon.

Bake for 25 minutes or until a toothpick inserted into the center comes out clean.

Cool for 10 minutes before serving.