In a small saucepan, stir the jelly over medium heat just until melted.

Off heat, whisk in the blackberry liqueur.

Divide the mixture among 4 coupe glasses or 4 small wide bowls and refrigerate until the jelly is firm, about 30 minutes.

In a small saucepan, bring 1 cup of prosecco just to a simmer over medium heat.

In a medium bowl, whisk together the sugar and gelatin.

Whisk this mixture into the hot prosecco, ensuring sugar and gelatin completely dissolve (2-3 minutes).

Remove from heat, gently stir in the remaining 1 1/2 cups prosecco (it will fizz up), and pour 1/2 cup into a small bowl.

Add 12 blackberries to the bowl and toss until coated.

Pour the remaining prosecco mixture over the set jelly in the coupe glasses.

Add 3 fresh berries to each glass.

Refrigerate until set, about 3 hours.

Refrigerate the blackberries in the small bowl, tossing often, until the berries are glossy and the gelatin begins to set, about 30 minutes.

Transfer the glossy berries to a plate and keep refrigerated.

Top each serving with a large dollop of sweetened whipped cream and the glossy blackberries.