Blackberry Refresher

Ingredients
750ml Prosecco
2 cups blackberries
3 oz sugar
1 1/2 tbsp rosemary (finely chopped)
2/3 cup water
Fresh rosemary sprigs and blackberries for garnish

Preparation
Simmer blackberries, sugar, water and rosemary in a small, uncovered saucepan, stirring occasionally for 20 minutes. The mixture should thicken and reduce by about 2/3. Pour through a sieve set over a glass and let stand 5 minutes (there will be about 1/3 cup). Cover and chill. Divide Prosecco and 1 1/2 tsp of syrup into each glass.