Arrange 24 small cups, or a silicone heart-shaped mold, on a tray that fits flat in the fridge.

Pour the boiling water over the gelatin powder in a large heatproof bowl and whisk for 2 minutes, until the powder is completely dissolved and the liquid looks clear, not grainy.

Stir in 1/2 cup cold water to cool the mixture slightly.

Stir in the champagne and vodka (if using) slowly, pouring down the side of the bowl so the gelatin doesn't foam over.

Pour the mixture into the cups or mold, filling each about three-quarters full.

Refrigerate uncovered for at least 4 hours, until the shots are fully set and spring back when touched lightly in the center.

Run a thin knife around the edge of each cup, or pop the hearts gently out of the silicone mold.

Garnish each shot with a tiny strawberry slice and a pinch of pink sanding sugar just before serving.