After greasing the baking pan, sprinkle with about 2 tablespoons flour. Working over the sink or a garbage can, tilt and turn pan, tapping gently, and coat butter with flour. Discard excess.
Spoon flour into a measuring cup and then level by sweeping a knife or spoon handle across top. This ensures that your flour doesn't get packed in, which can make the cake too dense.
Beat butter and sugar on high speed just until they turn pale and fluffy but are still grainy, about 3 to 5 minutes.