A 9-inch pan made of heavy-duty aluminum is the one for all your layer cakes. A good one has a straight side that is 2 to 3 inches high (deep enough so, if you have to, you can cut two layers from one cake) and a rolled rim. Buy two so you can bake two cakes — for a four-layer cake — at the same time. Real Simple pick: 9-by-3-inch round cake pan, $8, www.bridgekitchenware.com.