In a medium bowl, cream together the butter and sugar until light and fluffy.
Beat in the eggs, one at a time, mixing until fully incorporated; stir in the vanilla.
Combine the flour, baking powder and salt; stir into the batter alternately with the milk. If the batter is too stiff, a tablespoon or two of milk may be added.
Spread the batter evenly into the prepared pan.
Bake for 30 to 35 minutes in the preheated oven, until a toothpick inserted into the center comes out clean. Cool in pan on a wire rack, then turn out onto a serving plate. Dust with confectioners' sugar right before serving.