Combine water and sugar in a small saucepan over medium heat. Stir until sugar dissolves.
Add 1/2 cup blueberries and 2 thyme sprigs. Simmer for 10 minutes, then remove from heat.
Strain the syrup and let it cool completely. This can be made ahead and stored in the fridge for up to 1 week.
For each cocktail, add 1 oz blueberry thyme syrup and lemon juice to a shaker with ice. Shake for 15 seconds.
Strain into a champagne flute.
Then, top with prosecco and stir gently.
Garnish with fresh blueberries and a thyme sprig.
Notes
Make extra syrup to have on hand for future cocktails. The drink can be made non-alcoholic by replacing prosecco with sparkling water.Fresh blueberries work best, but frozen can be used for the syrup in winter months.The syrup needs to cool fully before using. Speed this up by placing it in an ice bath.Pre-chill the prosecco and glasses for the best results.