While the exact ingredients for a Tom and Jerry vary based on spices and liquor, a basic recipe includes eggs, sugar, rum, spices, vanilla flavoring and milk. Most recipes make batter for more than one drink, with specifications to turn that batter into the signature eggnog-like drink.
Begin by making the batter. Separate the eggs and whisk the yolks until they are thin. Add sugar, rum, spices and vanilla flavoring to the yolks, then beat with a handheld mixer. In another bowl, beat the egg whites until they form stiff peaks. Gently fold the whites into the yolk mixture, and refrigerate if not using immediately.
To make a Tom and Jerry, heat milk to a low boil over low heat. Stir the batter and add approximately 1.5 tablespoons of the batter to a large mug. If desired, heat the mug in the oven or by rinsing the mug with hot water before adding the batter. Pour rum into mug, stirring to achieve a smooth consistency.
When the milk is warm, pour it into the mug while continuing to stir to thoroughly blend all the ingredients. Add a dash of nutmeg to the top and serve while warm. Repeat with remaining batter to make additional drinks.