In a medium bowl, briskly whisk the egg yolks until they’re smooth and have lightened a bit in color, about 1 minute. Gradually whisk in the sugar, then continue to whisk until the mixture is thick and considerably lightened in color, about 2 minutes. Stash next to the cooktop.
Heat the half and half, nutmeg, and grains of paradise in a medium saucepan over medium-high heat until it begins to steam and registers around 165°F, about 7 minutes. Remove from the heat and, while whisking the egg mixture constantly, gradually ladle in about one-quarter of the hot dairy mixture.
Whisk the hot egg mixture into the remaining dairy mixture in the saucepan, set over medium heat, and cook, stirring frequently, until the mixture reaches 175 to 180°F, about 3 minutes. Meanwhile, place a second medium bowl inside a large bowl filled with ice. Set a fine-mesh sieve over the bowl.
Remove the saucepan from the heat, then pour the custard through the sieve into the bowl. Stir in the bourbon, rum, sherry, and vanilla. Continue to stir frequently until the mixture has cooled to at least room temperature, about 15 minutes. Consume immediately or transfer the bowl of nog to the fridge to chill completely. Add a little extra nutmeg over the top before serving if you so choose.