In a medium bowl, mix together the flour, baking powder, baking soda and salt.
In a large bowl, cream together the butter and sugar until light and fluffy. Beat in the eggs one at a time, then stir in the vanilla. Beat in the sour cream. Gradually add in the dry ingredients until just blended.
Spread batter into prepared pan.
Bake for 30 to 35 minutes in preheated oven, or until toothpick inserted into center of cake comes out clean.