In a mixing bowl, beat eggs at high speed until thick, about 5 minutes. Gradually add sugar, beating until mixture is light and fluffy. Combine flour and baking powder; add to batter with vanilla and beat at low speed or until smooth. In a saucepan, heat milk and butter just until the butter melts, stirring occasionally. Add to batter, beating until combined. Pour into a greased 13"x9"x2" baking pan. Bake at 350 for 30-35 minutes or until cake tests done. Cool on a wire rack.