Place the butter in the bowl of a stand mixer and attach the whisk. On medium speed, beat the butter until it is very creamy, about 3 minutes. (If you don’t have a stand mixer, a handheld mixer will do the trick as well.) Sprinkle in the sugar and continue to beat on medium speed until very fluffy and pale, about 3 minutes. Beat in the vanilla until just blended. Add 1 egg and beat on low speed, just until combined, about 15 seconds. Add the remaining eggs, one at a time, beating on low speed just until combined, about 15 seconds per egg, scraping down the bowl after each addition. Still on low speed, add half of the flour mixture; beat only until just blended, 30 to 45 seconds, scraping the bowl halfway through.