Cream butter in a large mixing bowl; gradually add 2 cups sugar, beating well. Add eggs, beating well.
Sift together flour, baking powder, and salt; add to creamed mixture alternately with milk, beginning and ending with flour mixture, mixing well. Stir in vanilla.
Pour batter into a well greased 10-inch Bundt pan. Bake at 325° for 55 minutes or until cake tests done. Cool in pan on a wire rack 10 minutes; invert cake onto wire rack, and cool completely. Prick cake several times with a wooden pick. Combine remaining sugar and lemon juice in a small mixing bowl; pour over top of cake. Garnish with lemon slices.