Q If a recipe calls for shortening, does it have to be solid fat such as Crisco, or can I use butter or oil?

A Shortening is always solid, made so by hydrogenation. It is 100 percent fat and can be replaced by a solid animal fat, such as lard or suet. Note that although butter is also solid animal fat, it has 20 percent water built in, which can upset the balance crucial to some baking recipes. Take care when converting to butter, and never use the soft oil-based spreads, which contain great amounts of water.

Oil, including butter oil (ghee), is 100 percent fat, but because of its liquidity, it will coat other ingredients, such as flour, differently. For that reason, it's never used in a recipe for pie crust or other flaky pastry items; the result won't be as tender or flaky.

It is better to stick to the recipe whenever possible.

Q In making fudge, I was hoping to be able to cut back on sugar and, therefore, calories, by choosing bitter, unsweetened chocolate instead of semisweet that the recipe called for. But to my surprise, the unsweetened variety had more calories. Is it the higher content of cocoa butter that accounts for it? Would using cocoa be a better choice?

A Dark unsweetened chocolate indeed is slightly higher in calories than semisweet. It is from the actual cocoa bean, since semisweet contains more -- not less -- cocoa butter. For less fat, dark is the way to go.

Anyway, if you are switching because of health concerns, you are on the right track. Numerous studies have shown that dark chocolate has more heart-friendly components than its lighter, sweeter cousins.

As for cocoa powder, it has the lowest calorie count with almost no cocoa butter, but still contains heart-friendly ingredients. It is the most suitable for dieters.

To substitute with cocoa powder, the recommended formula is 1 ounce chocolate equals 3 tablespoons cocoa powder plus 1 tablespoon oil. Use canola oil to keep the heart-healthy trail going.

Q The crust on my cake often separates from the body. What am I doing wrong?

A Baking a beautiful cake is science in action. There are some areas you should pay particular heed to. The first and most important is the oven temperature; the other is beating egg whites.

My suspicion is that the temperature in your oven is too high. When you put the cake in, it may rise nicely, but the very top layer of batter bakes up too fast, before heat can travel adequately by conduction toward the center.

When the cake cools and you cut it, the top may crumble and reveal a hollow space underneath. This overdose of heat on top can also happen if you place the pan too close to the top, because of excessive reflected heat. It is a good idea to check your oven with a good quality oven thermometer.

Since most cakes are foam cakes, how you beat the eggs also affects the outcome. Over-beating can result in some defects, including deflation within and drying out of the top layer, leading eventually to separation -- as well as a very tough cake.

The bottom line: Use a good recipe and follow good baking practices, including careful measurements, proper creaming of butter and sugar, gentle folding of whites and correct placement of the pan.