Prepare your favorite flavor Pillsbury Plus Cake Mix as directed on package.
Pour batter into one 8 or 9 inch round layer pan and one 8 or 9 inch square pan (both should be 8 or 9 inch, not one of each).
Bake as directed.
Cut round in half to form 2 semi circles, fitting cut edges to adjoining sides of square.
Frost with double recipe of favorite frosting, making sure that top and sides are completely covered.