Eggnog is a milk or cream-based beverage sweetened with sugar and spiked with spirits such as rum, brandy, whiskey or a combination thereof. Eggs, of course, are the main ingredient. And since eggs give eggnog its characteristic velvety texture and cloud-like froth -- the yolks build the custardy base and the whites add lightness -- there are no substitutions. Don't be afraid to play with milk-to-booze ratios, spirit selection/combination, and spice combinations to perfect the recipe for our own taste

Ingredients:
 1 quart heavy whipping cream (well chilled)
12 large eggs*, separated
12 tablespoons granulated suger (3/4+ cup)
 1 pint dark rum ("Goslings Black Seal" strongly recommended)
    (taste first, but add more if your taste buds require)
 1 pint whole milk (or less as needed)
   Nutmeg (for "pretty" and/or taste)

1. Separate eggs
2. Whip sugar with egg yokes until color is lighter and double in size.
3. Mix or whisk in rum (pour very slowly) until thoroughly combined (this should take about 90-120 seconds; if done too fast you will curdle the yokes)
4. Whip cream until soft peaks.
5. Whip egg whites until soft peaks.
6. Fold egg whites into whipped cream.
7. Fold rum / egg yoke misture into cream.
8. Taste.
     At this point, either pour into a punch bowl if being served immediately, or if desired into a sealable container and store overnight in the refrigerator.
9. Pour into punch bowl.
10. Fold milk a little at a time for taste and just enought to thin.
11. Add nutmeg to tope once in punch bowl.

Courtesy of Newton Richards

You can also top it with whipped cream and add a cinnamon stick, but Newt's recipe doesn't need anything else.

See also:
5 Things You Didn't Know You Could Make With Eggnog | The Odyssey