Combine butter and 1 cup sugar in a medium mixing bowl, stirring until well blended. Add 1 egg and egg yolk; mix well. Combine flour, baking powder, and salt; add to butter mixture, mixing well. Stir in 1 teaspoon vanilla. Spread mixture evenly in a greased 13- x 9- x 2-inch baking pan; set aside.
Lightly beat 1 egg white (at room temperature); gradually add brown sugar, beating well. Stir in pecans and remaining vanilla. Spread pecan mixture evenly over prepared crust. Bake at 375° for 15 minutes; reduce temperature to 325°, and bake 20 minutes. Cool completely in pan on a wire rack, and cut into 2-inch squares.