Pour 1/2 cup champagne into a small bowl and sprinkle the gelatin evenly over the top; let it sit 5 minutes, until softened and spongy.

Heat water and sugar in a small saucepan over medium heat, stirring until the sugar dissolves, about 2 minutes; do not let it boil.

Remove from heat and whisk in the bloomed gelatin until fully dissolved and the liquid is clear.

Let the mixture cool to room temperature, about 10 minutes, then stir in the remaining 1 1/2 cups champagne gently to avoid losing the bubbles.

Drop two or three raspberries into each of six coupe glasses.

Pour the champagne mixture evenly over the berries, filling each glass about three-quarters full.

Refrigerate for at least 4 hours, until the gelée is fully set and springs back lightly when touched.

Just before serving, scatter edible gold leaf flakes over the surface of each gelée, where they will float and catch the light.