How to Make It
Prepare Filling: Bring first 3 ingredients and 3 cups cranberries to a boil in a medium saucepan over medium-high heat. Boil, stirring often, 5 to 6 minutes or until cranberries begin to pop. Transfer 1 cup cranberry mixture to a small bowl, and stir in remaining 1/2 cup whole cranberries. (This will be the Cranberry Topping.) Transfer remaining hot Cranberry Filling mixture to another small bowl. Cool both mixtures completely (1 hour). Cover; chill 8 hours.
Prepare White Cake: Preheat oven to 325°. Beat butter at medium speed with an electric stand mixer until creamy. Gradually add sugar, beating until light and fluffy. Add orange zest and vanilla; beat until blended. Combine 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 after each addition. Beat egg whites at high speed until stiff peaks form. Stir about one-third of egg whites into batter; fold in remaining egg whites in 2 batches. Spoon into 3 greased (with shortening) and floured 9-inch round cake pans. Bake at 325° for 25 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 (about 1 hour).
Prepare Buttercream: Beat butter and next 2 ingredients at medium speed with an electric mixer 1 to 2 minutes or until creamy. Gradually add powdered sugar alternately with orange juice. Beat at low speed until blended and smooth after each addition. Stir in vanilla. If desired, add 1 to 2 Tbsp. milk, 1 tsp. at a time, beating until frosting reaches desired consistency.
Place 1 Basic White Cake layer on a serving platter. Spoon 1 1/2 cups buttercream 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. Spread cake layer with half of chilled Cranberry Filling (without whole berries), spreading to edge of piped frosting. Top with second cake layer. Repeat procedure with frosting and remaining Cranberry Filling (without whole berries). Top with third layer. Spread remaining buttercream over top and sides of cake. Pipe a ring of frosting around top cake layer just inside the top edge. Spread Cranberry Topping (with whole berries) over top cake layer, spreading to edge of piped frosting.
Cake layers may be baked in 3 (8-inch) square disposable aluminum foil pans. Increase bake time to 26 to 30 minutes.