For the cocktail:

1. Add persimmon simple syrup to the bottom of a champagne flute.
2. Add gin. Fill the glass with Champagne or dry Prosecco.
3. Garnish with an 1/8 slice of persimmon.

For the syrup:

1. Smash 4 extra-ripe persimmons with a fork to macerate the fruit.
2. Add to a saucepan with 1 cup boiling water and 1 cup sugar. Bring to a boil and stir until sugar is dissolved. Let stand and bring to room temperature.
3. Pass through a fine sieve and decant into a clear jar with lid. This can be made ahead of time and stored in the refrigerator for up to 1 week.