Prep the chocolate rim: Melt a small handful of chocolate chips in the microwave in 15-second bursts, stirring until smooth.
Dip the rims of heat-safe martini or coupe glasses into the chocolate, then into crushed cookies, cocoa powder, or sprinkles. Set aside to firm up.
Warm the cocoa base: In a small saucepan, heat 3/4 cup milk over medium-low until steaming. Whisk in 2–3 tablespoons hot cocoa mix (or 2 tablespoons cocoa powder plus 1–2 tablespoons sugar).
Heat gently; do not boil.
Add the spirits: Remove from heat. Stir in 1 ounce chocolate liqueur and 1–1.5 ounces vanilla vodka. If using coffee liqueur, add 1/2 ounce.
Taste and adjust sweetness with a little more cocoa mix or sugar if needed.
Whip the topping: If not using ready-made whipped cream, shake 1/4 cup heavy cream in a sealed jar for 30–60 seconds until thick and spoonable, or whisk lightly to soft peaks. Add a splash of vanilla and a pinch of sugar if you like.
Assemble: Pour the hot cocoa martini into the prepared glass. Top with a generous dollop of whipped cream.
Finish with a pinch of cinnamon or nutmeg, a few mini marshmallows, or a tiny sprinkle of sea salt.
Serve immediately: This drink is best hot, with the rim intact and the whipped cream just starting to melt into the cocoa.