Cupcakes:

1 1/2 cups self-rising flour
1 1/4 cups all-purpose flour
1 cup (2 sticks) unsalted butter, softened
2 cups sugar
4 large eggs, at room temperature
¾ cup eggnog
¼ cup milk
1 teaspoon vanilla extract
Spice Rum Buttercream:

5 large egg whites
11/2 cup sugar
4 sticks unsalted butter, diced and softened
1/4 teaspoon salt
½ cup spiced rum