That's not to say your teacher was wrong, either. You are looking at different kinds of fats. Pure vegetable oil has 124 calories per tablespoon, no matter whether it's corn oil, olive oil or mustard seed oil. So your teacher is right. But butter, even if it is pure "real" butter, is not pure fat. It's only about 81 percent fat. Butter has about 1 percent protein. If you've ever melted butter and watched it start to brown, the little brown specks are the protein browning. Protein has fewer calories than oil.

Also, butter is a little more than 15 percent water. When you melt butter in a frying pan and it sizzles and hisses, that's the water cooking off. Water has no calories. So when you reduce the calories by the amount of water and protein, a tablespoon of butter has only 100, compared to 124 for pure oil or pure butter fat.

If you look at some of the "lite" margarines, the calories are reduced in those by all the extra water that has been beaten into the fat. Whipped butter and margarine have extra air beaten into them. Neither air nor water cook the same way fat does, so you can see why you can't bake with lite or whipped margarine in a regular recipe.

But for the calories, believe what the Nutrition Facts box says, because products are so different.

Q: I use evaporated milk for some of my baking, but one can is usually more than I need. How long can I keep it in the refrigerator? Can I freeze the extra for later?