Cheesecakes are among the richest and most decadent of desserts, best savored slowly in small bites with a cup of strong coffee at your elbow. They're surprisingly easy to make, consisting mostly of eggs, sugar and some form of soft cheese. That simplicity of ingredients, unfortunately, is countered by the unexpected difficulty of baking one correctly. Unlike ordinary cakes, you can't test one with a toothpick; you must instead pull it from the oven when it's slightly -- and very visibly -- underdone.
The Cheesecake Conundrum
The important thing to remember about cheesecake is that, despite its name, it isn't really a cake. In truth it's a custard, like quiche or creme brulee. Its primary thickener isn't a starch -- though some recipes call for small quantities of cornstarch or flour -- but eggs. As the eggs gently heat in your oven, they begin to thicken and coagulate, setting your cheese mixture to its characteristics soft-but-firm texture. The liquid filling retains heat for a significant time after you remove it from the oven, so if you bake it until it appears done, it's too late. A perfectly baked cheesecake shows a 2 1/2- to 3-inch circle in its center that's still very jiggly, almost liquid, when you take it from the oven.
The Water-Bath Workaround
You can test the cheesecake with an instant-read thermometer, which should show an internal temperature of 150 degrees Fahrenheit when the cheesecake is properly cooked. Unfortunately -- a cruel irony -- the thermometer itself can cause the cheesecake to crack. To purchase some margin for error and give your cheesecake a finer texture, bake it in a water bath as you would with many other custards. Wrap the bottom of your springform pan in a sheet of aluminum foil, to prevent water from seeping in, then place it in a roasting pan. Slide your roaster into the oven, then carefully pour in enough boiling water to match the depth of the cheesecake's filling. The water moderates the oven's temperature and makes it harder to overcook your cheesecake.