I actually hate eggnog, so if I were to make it, it would probably be this recipe, from Homemade Liqueurs by Dona and Mel Meilach, because it is one serving and mostly alcohol. The orange liqueur recipes in the book have a base of about 3/4 vodka to 1/4 simple syrup. I don't know how that will compare to commercial products such as Grand Marnier, Curaçao, or whatever else you'd be using, so you should maybe add some simple syrup or other sweetener to taste.
1/4 oz. orange liqueur
1 fresh egg
3/4 oz. brandy
1/4 oz. milk
Shake well with ice and strain into glass. Sprinkle grated nutmeg on top.
If I something fancy and time-consuming, I would make this recipe from Cosmo Cookery, because to the best of my knowledge it's the only eggnog recipe approved by the late Helen Gurley Brown! The book says that this recipe is very rich and should be served in small glasses, and will make approximately 15 servings. This seems a lot of servings for a book with the subtitl "Gourmet Meals from the First Drink to the Last Kiss," so I guess this was for a holiday orgy.
6 egg yolks
1/2 cup sugar
1 cup brandy or bourbon whiskey
2 cups cream
2 cups milk
3 egg whites
Freshly grated nutmeg
In a large, deep bowl, beat egg yolks until creamy and light-colored. Gradually beat in sugar. Add slowly 1 c. brandy, 1 c. cream, and 2 c. milk. Continue beating as you add all these ingredients. In a separate bowl beat the egg whites until very stiff. Gently fold the egg whites into the whipped cream, then blend them into the first mixture. Grate nutmeg over each serving.
It is one of the best book covers ever.