To save time, let the eggs, buttermilk, and butter come up to temperature while the browned butter and spice mixture cools. To prevent unsightly air holes in the finished cake, be sure to follow the instructions for removing air bubbles in the batter (see illustrations below). Leftover cake can be stored, covered with plastic wrap, in the refrigerator for up to 2 days. The cake should be brought to room temperature before serving.