Bloom the gelatin: Sprinkle gelatin evenly over the cold water in a small bowl. Let it sit 5–10 minutes until fully absorbed and jelly-like. No stirring frenzy needed.
Warm the base: In a medium saucepan, combine heavy cream, whole milk, sugar, and a pinch of salt. Heat over medium, stirring, until the sugar dissolves and steam appears. Do not boil. If it’s bubbling, it’s too hot.
Add the eggnog: Stir in eggnog and heat gently until warm again, about 2–3 minutes. You want it hot enough to melt gelatin, not simmering.
Melt in the gelatin: Remove the pan from the heat. Add the bloomed gelatin and whisk until completely dissolved. If you see any tiny granules, keep whisking—they must vanish.
Flavor boost: Stir in vanilla and an optional pinch of cinnamon. Taste carefully. If your eggnog is very sweet, you can add a splash more milk to balance.
Strain for silk: Pour the mixture through a fine-mesh sieve into a large measuring cup or bowl with a spout. This removes any undissolved bits and guarantees a silky set.
Portion and chill: Divide the mixture into 6–8 small ramekins or glasses. Let cool at room temp 15 minutes, then cover and refrigerate at least 4 hours, preferably overnight, until softly set.
Finish with nutmeg dust: Just before serving, sprinkle each panna cotta with a light veil of freshly grated nutmeg. Add whipped cream or a crunchy garnish if you’re feeling fancy.
Unmolding option: To unmold, dip each ramekin in warm water for 10–15 seconds, loosen the edge with a thin knife, and invert onto a plate. Tap gently. If it refuses, give it another quick dip.