To a medium size saucepan add the blackberries, sugar, lemon juice and water. Bring to a boil and stir occasionally. Boil for about two minutes then remove from heat and allow to cool slightly. Strain through a sieve to remove seeds and refrigerate until ready to make cocktails. Syrup is good for about two weeks stored in the refrigerator.
For the cocktail put 1-2 teaspoons of the syrup into the glass then pour in the prosecco. Add the blackberry garnish and thyme sprig
If you have extra syrup left over, and you will, you can use it on top of ice cream or pancakes. It would be wonderful.