Preheat oven to 350°. Beat butter at medium speed with an electric mixer until creamy; gradually add sugar, beating until light and fluffy. Add egg yolks, 1 at a time, beating until blended after each addition.
Stir together flour and next 2 ingredients; add to butter mixture alternately with milk, beginning and ending with flour mixture. Beat at low speed just until blended. Stir in zest and juice.
Beat egg whites in a large bowl at high speed until stiff peaks form. Gently stir one-third of egg whites into batter; fold in remaining egg whites. Spoon batter into 4 greased (with shortening) and floured 9-inch round cake pans.
Bake at 350° for 16 to 20 minutes or until a wooden pick inserted in center comes out clean. Cool in pans on wire racks 10 minutes; remove from pans to wire racks, and cool completely.
Place 1 cake layer on a serving platter, and spread with about 1/2 cup Strawberry-Lemonade Jam, leaving a 1/2-inch border around edges. Spoon 1 cup Strawberry Frosting into a zip-top plastic freezer bag. Snip 1 corner of bag to make a small hole. Pipe a ring of frosting around cake layer just inside the top edge. Top with second and third cake layers, repeating procedure with filling and frosting between each layer. Top with last cake layer, and spread remaining Strawberry Frosting on top and sides of cake.