Prepare cake recipe as directed.
Pour batter into greased 9-inch-square cake pan; bake as directed.
Remove from pan; cool.
Cut in half horizontally. (Save half for future use.)
Place on heatproof platter.
Beat egg whites until foamy.
Add cream of tartar; mix in.
Add sugar gradually, continuing to beat until egg whites form stiff peaks.
Remove ice cream from container; round ice cream corners with small spatula.
Place on cake.
Cover ice cream and cake generously with meringue; be sure to smooth and cover entire surface.
Working quickly, fill pastry bag with meringue.
Using rosette tip, decorate baked Alaska as illustrated.
Place in preheated 400 °F oven 3 minutes or until meringue just begins to turn brown.
Decorate with spring flowers.