1. The butter needs to be at room temperature. That means you need to be organized and have it out of the fridge for about 30 minutes before you use it. If you are not organized, a tip that works well is to microwave the stick of butter for 5-10 seconds. You want the butter to be soft enough that when touched it will leave an imprint in the butter. If the butter is too soft it will cause the final product to be dense when baked.
2. How long to beat the butter and sugar and at what speed. If your butter is the correct temperature and you have a stand mixer like a Kitchen Aid mixer, chop up the butter into hunks then place the butter into the bowl. Beat the butter alone for 10 seconds with the paddle attachment to break up the butter. Next gradually add the sugar in a steady stream as the mixer is running on a medium speed around 3# or 4#. If you have a hand mixer you will need to beat at a higher speed but the instructions are the same. After all the sugar is added beat for 1 minute at a medium speed (3# - 4#) on your Kitchen Aid. Stop your mixer and scrap down the sides and bottom of the bowl to make sure everything is incorporated. Start your mixer again at a medium speed and beat for another minute. Total beating is 2-3 minutes at a medium speed. With a hand mixer use a higher speed and beat for 5 minutes, scraping down the bowl half way thru the process. Beating too little or at a high speed will effect the density of your final product because it does not aerate the butter properly.
How do you know it's done:
-Under-creamed and your mix will feel like wet sand or damp cornmeal. -Over-creamed, and your mix will have the feel of oil and sugar on your fingers, rather like a facial scrub.
-Your well-creamed mix will be moist and light and the sugar will be nearly dissolved. You’ll barely feel any grit when you rub it between your fingers.
Using whole grain flour is more difficult to get a light cake because the whole grain has the germ (oil) and the bran. Mastering this simple technique ensures that even when your cake or muffin is 100% whole grain it will be light and tender.
King Author Flour Author Mary Jane Robbins