The Tom & Jerry from No. 9 Park has a cult following, but this warm and frothy cocktail is only served under the right conditions. Firstly, it must be between November 1 and February 13. Secondly, it has to be snowing, and that snow has to stick.

No exceptions are allowed—unless you prepare it at home, of course.

What truly makes this rum-and-Cognac drink unique is the “Tom & Jerry batter,” a mix of egg whites whipped into a frothy meringue and egg yolks blended with a cinnamon-y spice mix, which bar manager Jared Conklin prepares to taste with each batch. “At home if you prefer other spices you can always add to it,” Conklin says.

To heat the drink, he adds the spirit and batter to a small tin shaker, which is held inside a Moscow Mule mug filled with warm water (for a kind of bain-marie). Once warmed, he tops the mixture with steamed milk and garnishes it with fresh nutmeg.

It may look like an eggnog, but it’s airy and fluffy rather than heavy and rich, while still packing all the holiday spice notes you’re craving.

You could kick it up a notch by making “the stronger version.” This industry-favorite variant calls for equal parts Green Chartreuse and navy-strength Smith & Cross Jamaican rum for its spirit base.

“If anyone is asking for the ‘other version’ of the Tom & Jerry, you’re like ‘Ok, you want the boozier version,’” says Conklin. “There’s not a name that’s been coined or anything like that—it’s one of those unspoken things.”

Tom & Jerry
3 ounces steamed milk
2 ounces Tom & Jerry batter*
1 ounce Plantation Barbados 5 Years Rum
1 ounce Pierre Ferrand 1840 Cognac
Freshly ground nutmeg, for garnish

Add 1 ounce of spirit followed by 1 ounce of Tom & Jerry batter to a mixing glass surrounded by hot water; repeat until all spirits and batter have been added. Stir to combine ingredients and slowly warm mixture. Once mixture has warmed evenly, pour into a heated mug and fill to the top with steamed milk. Garnish with freshly ground nutmeg.

*Tom & Jerry Batter (yields about 1 quart)
For a more flavorful spice mix, Conklin recommends grinding spices yourself with a mortar and pestle and then straining the mixture through a chinois.

3 eggs
1 cup sugar (divided)
1 barspoon (just over a teaspoon) ground spice mix (2 parts cinnamon; 1 part blend of nutmeg, clove, allspice, and mace to taste)

Carefully divide the egg whites and egg yolks into two separate bowls. Using a stand mixer, whip the egg whites slowly while incorporating ½ cup sugar until a meringue with high, stiff peaks forms. Add spice mix to egg yolks and use stand mixer to incorporate the final ½ cup of sugar. Carefully fold the egg white mixture into the egg yolk mixture. Add to a container, seal, and refrigerate. Use within 1 day.