It’s a myth that butter needs to be at room temperature for baking. No doubt warm butter is easier to beat, but with today’s monster mixers, that’s hardly necessary.
Warm butter can’t trap air as well, resulting in flat cookies and cakes that don’t rise. Instead cut your well-chilled butter into pieces then beat with a mixer until smooth.
—From Lobsters Scream When You Boil Them and 100 Other Myths About Food and Cooking (Gallery Books, 2011) by Bruce Weinstein and Mark Scarbrough.