Step 1

Position a rack in the center of the oven. Preheat the oven to 350°F (325°F for a convection oven). Grease three 9- by 1½-inch round baking pans or two 9- by 3-inch round baking pans or springform pans, line the bottoms with parchment paper or wax paper, grease again, and dust with flour.To make the batter: Sift together the flour, baking powder, salt, and, if using, nutmeg.

Step 2

In a large bowl, beat the butter on low speed until smooth, about 2 minutes.

Step 3

Increase the speed to medium, gradually add the sugar, and beat until light and fluffy, about 5 minutes. Add the vanilla.Add the flour mixture and milk alternately (4 portions for the flour; 3 portions for the milk) beginning and ending with the flour.In a large bowl, beat the egg whites on low until foamy, about 1 minute. Increase the speed to medium and beat until soft leaks form, 5 to 8 minutes. Fold one fourth of the egg whites into the batter, then gently fold in the remaining whites.

Step 4

Divide the batter equally between the prepared pans. Bake until a tester inserted in the center comes out clean and the cake springs back when lightly touched, 20 to 25 minutes for 3 pans or about 30 minutes for 2 pans.

Step 5

Let cool in the pans for 10 minutes, then remove to wire racks and let cool completely, at least 1½ hours. The cake can be wrapped and stored at room temperature for up to 1 day.

Step 6

Place the egg yolks in a 2-quart saucepan and lightly beat. Add the sugar and beat until smooth. Add the butter and salt and cook over medium heat, stirring constantly with a wooden spoon, until thick enough to coat the back of the spoon and almost translucent, about 10 minutes. Do not boil.

Step 7

Remove from the heat and gradually stir in the bourbon and vanilla. Add the raisins, pecans, and, if using, coconut and/or cherries. Let cool, but do not chill before spreading.

Step 8

If using 2 larger pans, use a serrated knife to cut each cake in half horizontally. Arrange a cake layer on a serving plate and spread with a third of the filling, about 1 cup. Top with a second cake, spread with half of the remaining filling, and place the third cake layer on top. If making a 3-layer cake, spread the remaining filling on top; for a 4-layer cake, leave the top bare and cover later with frosting. Place in a covered container. Let ripen in a cool place or the refrigerator for at least 2 days and up to 2 weeks, daily spooning any of the filling that seeps out back over top of the cake. For long term storage, place in the freezer for up to 4 months.

Step 9

In a small saucepan, stir the sugar and water over low heat until dissolved. Stop stirring, increase the heat to medium-high, and boil until it reaches the soft-ball stage and registers 238°F on a candy thermometer.

Step 10

Meanwhile, in a large bowl, beat the egg whites on low speed until foamy, about 1 minute. Add the salt or cream of tartar, increase the speed to medium-high, and beat until soft peaks form, about 1 minute.In a slow, steady stream, beat in the hot syrup. Be careful the syrup does not touch the beaters or it will spin into threads. Add the vanilla and beat until cool.

Step 11

For a 3-layer cake, spread the frosting over the sides of the cake; for a 4-layer cake, spread over the sides and top. If not serving on the same day or for leftovers, store in the refrigerator covered with a cake keeper, a tent of foil, or a bowl with a knife or other flat utensil wedged under it. Serve at room temperature.