eggnog recipe

4 large egg yolks - 1/2 cup granulated sugar - 2 cups whole milk - 1 cup heavy cream - 1/2 teaspoon ground nutmeg - 1/4 teaspoon ground cinnamon - 1 teaspoon vanilla extract - 1/2 cup rum, bourbon, or brandy (optional) - 4 large egg whites - 2 tablespoons granulated sugar