This is an elegant, refreshing dessert — a cross between a Kir Royale and a gelatin fruit dessert. It’d be great for a summertime celebration or simply at brunch.
Use a melon baller to portion the melon into small round balls. Divide the melon balls and half the raspberries evenly among 4 tall narrow glasses or dessert cups, about 8 ounces each.
Sprinkle the gelatin over 1 cup of the Prosecco and stir to combine (fresh sparkling wine will bubble up, so do this in a medium bowl with room for froth). Let stand until the gelatin softens, about 5 minutes.
Toss the remaining raspberries with the sugar and water in a medium saucepan and heat over low heat until raspberries break down and sugar dissolves, about 5 minutes. Pour off about 3 tablespoons of the raspberry juice, and reserve for flavoring the whipped cream.
Add the remaining Prosecco to the berries in the saucepan and heat over medium-low until the berries break up and flavor the wine, about 2 minutes. It’s best not to let the wine boil. Stir in gelatin mixture until dissolved, about 1 more minute. Strain and press through a fine mesh strainer to remove any fruit pips. Pour Prosecco gelatin into glasses over the fruit and refrigerate until set, about 3 hours.
Just before serving whip the cream and sugar until soft peaks form. Fold in the reserved raspberry juice. Dollop the cream on top of each set gelatin and serve.