Butter

One of the basic techniques that frequently gets overlooked is how to cream butter.

Baked goods that have butter in them, but are not creamed properly, are often dense, and sometimes don't even come out properly at all.

For example, when I was first baking the Magnum Opus Chocolate Chip Cookie, my creaming technique was so bad that the 8 oz cookie would spread all over the pan into a thin sheet of burnt cookie.

What was going on here?

For you to cream butter, you need to wait for butter to come to room temperature. If you don't, when you beat in the sugar, the sugar fails to make the air pockets in the mixture that make the mixture "light and fluffy" (possibly one of the most repeated phrases in baked goods recipes). I don't know why this is the case. It's science!

Waiting the hour or so necessary for the butter to come to room temperature can be one of the most infuriating thinking ever. "I'm ready to make cookies right now!" But there's really no shortcut to warming butter (don't put it in the microwave!) other than to cut it up into small dice or grating it. Just wait. Otherwise, you're gonna get humbled.

More: http://www.baking911.com/howto/cream.htm