Crack all 12 eggs into a large heatproof bowl and whisk until yolks and whites are fully combined.

Add the granulated sugar to the eggs and whisk vigorously for about 2 minutes until slightly pale and sugar begins to dissolve.

Fill a pot with 2 inches of water and bring to a gentle simmer, then place the bowl on top ensuring the bottom doesn’t touch the water.

Whisk constantly and heat the mixture until it reaches 160°F (71°C), then remove from heat immediately.

Let the egg mixture cool to room temperature, stirring occasionally, then strain through a fine-mesh sieve into another bowl.

Pour in heavy cream and whole milk and whisk until fully incorporated and mixture is uniform.

Whisk in whiskey, dark rum, vanilla extract, ground nutmeg, cinnamon, cloves, and salt until spices are evenly distributed.

Transfer eggnog to a glass pitcher or bottle, refrigerate for at least 2 hours or overnight, then taste and adjust seasoning before serving.