Eggnog Cocktail

Whisk egg yolks and sugar in a medium bowl until pale yellow and smooth, 1 to 2 minutes.

Set a fine-mesh sieve over a bowl and place it near the stove. Heat milk and nutmeg in a medium saucepan over medium-high heat until steaming, about 10 minutes. Remove from heat. Whisking constantly, ladle 1/4 cup of the hot milk into the egg mixture. Continue to add the hot milk, 1/4 cup at a time, until all of it has been whisked in.

Return the mixture to the pan and cook over medium heat, stirring constantly with a wooden spoon, until the custard thickens enough to coat the back of the spoon and the temperature reaches 160°F, about 1 minute. Do not let it boil. Working quickly, pour the custard through the sieve into the bowl. Stir in vanilla. Transfer the eggnog base to a heatproof storage container and refrigerate until cold, 4 hours or up to 2 days.

Stir bourbon (or rum) into the eggnog base. Lightly whisk cream until foamy and stir into the eggnog. Garnish with more nutmeg, if desired. To prepare just one cocktail: Combine 1/2 cup eggnog base, 3/4 ounce bourbon (or rum) and 1 1/2 teaspoons cream in a cocktail shaker. Shake vigorously. Pour into a glass and garnish with nutmeg.