Preheat oven to 350 degrees. Cream together butter and sugar. Mix in eggs. Sift together flour, baking powder and salt. Add dry ingredients to wet. Stir in milk, vanilla extract. Butter a 9 inch square baking dish and line with pitted cherries. Pour batter over cherries and bake 30 minutes, until cake tester comes out clean. Dust with sifted powdered sugar while cake is cooling.