Eggnog Magic Cake

Finally, eggnog can be eaten. One magic cake batter turns into two layers when baking and cooling:a cake and a layer of custard. This dessert looks complicated to prepare, but it's actually very simple thanks to the available ingredients. Try it with a whipped cream top made by whipping heavy cream and bourbon until stiff peaks form. Would you like some more?" Try 20 eggnog desserts to sweeten the festive season next year.
Preheat the oven to 325°F. Brush an 8-inch square baking dish with butter.Pour the eggnog into a microwave-safe bowl and reheat in the microwave on MEDIUM-HIGH (50% power) at 15-second intervals until it is just slightly warm, about 1 minute and 15 seconds. Whisk with bourbon and vanilla; set aside.Whisk the egg whites and tartar in the bowl of a heavy-duty mixer with a whisk attachment on high speed until stiff peaks form, about 4 minutes. Transfer the egg-white mixture to a separate bowl and set aside.In the bowl of a stand mixer, wipe dry; add the egg yolks and 1 1/2 cups powdered sugar and beat on high speed until very light yellow, about 2 minutes. Add the melted butter and beat until smooth, about 30 seconds.Add the flour to the egg-yolk mixture in 3 batches, beating until smooth after each addition, and stopping wiping the sides of the bowl after the last addition to completely mix. Using a mixer running over low heat, gradually add the eggnog mixture until smooth. (The dough will be very thin.)Using a rubber spatula, add one-fourth of the egg white mixture to the egg yolk mixture; repeat with the remaining egg white mixture. (The dough should still be runny, with a few lumps of egg white.)Pour the batter onto the prepared pan and bake in the preheated oven until the top is browned and the middle is slightly convex, 50 to 55 minutes. Cool completely on a wire rack for about 3 hours. Or chill on a wire rack for 30 minutes, then transfer to the refrigerator to cool for at least 1 hour. Cut into 9 squares and sprinkle with nutmeg and remaining 1/4 cup powdered sugar.