These recipes call to cream the butter and sugar together for 6 to 8 minutes, an inordinately long time for a cake recipe. Because traditional pound cakes don’t use chemical leavening, all their lift comes from the air whipped into the butter and sugar during this step, so it’s important to get as much air in the batter as possible. The long beating time ensures this lift and that the butter and sugar will easily absorb the eggs and other ingredients, producing a supersmooth, even crumb once baked.