Sift together into mixing bowl flour, sugar, baking powder, and salt. Add brown sugar, shortening, peanut butter and milk. Beat 1 1/2 minutes. (With electric mixer, blend at lowest speed, then beat at a low speed. Or beat 225 strokes with a spoon.) Add eggs and vanilla. Beat 1 1/2 minutes. Turn into two 9-inch round layer pans, well greased and lightly floured on the bottoms. Bake at 375 degrees for 30 to 35 minutes until cake springs back when touched lightly in center. Cool. Place one layer, top-side down, on serving plate. Spread with peanut butter then with jelly. Top with second layer; frost.

Fluffy Frosting: Combine in top of double boiler sugar, corn syrup, water, egg whites, salt and cream of tartar. Cook over rapidly boiling water, beating with electric mixer or rotary beater until mixture stands in peaks. Remove from heat. Add vanilla; beat unitl frosting holds deep swirls.