Place the champagne and sugar in a saucepan. Remove 2 tablespoons of the champagne to a small condiment bowl; sprinkle the powdered gelatin over the champagne in the bowl. Let stand until set, about 1 minute.
Gently heat the champagne and sugar together, stirring constantly, until the sugar dissolves. Do not boil. Add the bloomed gelatin and stir until melted. Let stand until room temperature, about 20-25 minutes, or until barely warm to the touch (hot liquid will pop the boba). Transfer the mixture to a glass measure with a pour spout.
Drain the boba in a sieve and place them on paper towels. Gently transfer and evenly divide spoonfuls of the boba between each of 18 shot glasses (1.75 capacity each). Pour the champagne over the boba. Place in the refrigerator until set, about 2 hours.
In the bowl of an electric mixer, beat the heavy cream to soft peaks. Transfer to a piping bag or to a zip-top bag with a corner snipped. Pipe the whipped cream on top of the jelly. Sprinkle with nonpareils and gold stars. Refrigerate until ready to serve.
Just before serving, garnish with sprigs of rosemary, if desired.
Keyword bursting boba, champagne jelly, jello shots, new year's eve dessert