Set up your base: In a medium saucepan, add the milk and cream. Warm over medium-low heat until steaming, not boiling. You should see wisps of steam and small bubbles around the edges.

Whisk the yolks and sugar: In a mixing bowl, whisk egg yolks, sugar, salt, nutmeg, and cinnamon until smooth and slightly lighter in color, about 30–45 seconds.

Temper the eggs: Slowly ladle about 1/2 cup of the hot milk mixture into the yolk mixture while whisking constantly. Add another 1/2 cup in a thin stream, whisking. This prevents curdling.

Thicken gently: Pour the tempered yolk mixture back into the saucepan. Cook over low heat, stirring constantly with a spatula, until the creamer lightly coats the back of a spoon, 5–7 minutes. Do not let it boil.

Finish the flavor: Remove from heat. Stir in vanilla and, if using, a splash of bourbon, rum, or brandy. Taste and add a pinch more nutmeg if you like it spicier.

Strain and cool: Pour the mixture through a fine-mesh strainer into a clean jar or bottle to catch any tiny bits of cooked egg. Let it cool to room temperature, then cover and refrigerate until chilled, at least 2 hours.

Serve: Shake well before using. Start with 1–2 tablespoons per cup of coffee and adjust to taste.