Wash the quince thoroughly with a brush, peel off the skin, cut in half, remove the core and seed pod. Rinse the mint in cool water and shake off. Prepare three bowls for hardening the jelly.
Dissolve gelatin. Pour 3 tbsp into a small container. l. champagne and pour gelatin into it. Leave the gelatin to swell for 10-15 minutes, and then melt in a water bath, stirring constantly. Pour the remaining champagne into a saucepan, add sugar and place over medium heat. Stirring, bring the sugar to dissolve and pour the diluted gelatin into the champagne. Mix the mixture well and remove from heat.
Prepare quince jelly. Cut the quince into small cubes and place equally in three bowls. Pour champagne with gelatin over the quince, let cool slightly and put in the refrigerator until completely solidified for 3-4 hours.
Serve the finished jelly directly from the refrigerator, garnished with sprigs of fresh mint.