In a small saucepan, whisk together the whole milk, unsweetened cocoa powder and granulated sugar until smooth. Warm over medium-low heat until steaming but not boiling (about 4–6 minutes), whisking frequently to prevent scorching.

Finish the nog

Remove the saucepan from heat. Whisk in the egg nog, vanilla extract, a pinch of ground cinnamon and a pinch of ground nutmeg until fully incorporated and smooth. Taste and adjust sweetness or spices as desired.

Add liqueur

Divide the hot chocolate-nog base between two heatproof mugs (about 1 cup per mug). Stir 1 tablespoon (2 tbs total used above equals 1 tbs per serving) of Marie Brizard Chocolat liqueur into each mug. If serving nonalcoholic, omit the liqueur and replace with 1–2 tablespoons additional milk or egg nog per mug.

Whipped Cream Topping

Make whipped cream

Place the chilled heavy cream in a medium bowl. Add the powdered sugar and vanilla extract. Whip with a hand mixer or whisk until soft peaks form (about 1–2 minutes with a mixer). Do not overbeat; you want a light, spoonable cream.

Top the drinks

Spoon or pipe a generous dollop of whipped cream onto each hot chocolate nog, covering most of the surface.

Garnish

Sprinkle a pinch of freshly grated dark chocolate or chocolate shavings over the whipped cream, then dust lightly with ground nutmeg. Serve immediately while hot.