Make the lavender syrup first. Combine water and sugar in a saucepan over medium heat. Stir until the sugar dissolves.
Add dried lavender and simmer for 5 minutes. Then, remove from heat and let it steep for 30 minutes.
Strain the syrup through a fine-mesh strainer. Let it cool completely.
Fill a cocktail shaker with ice. Then, add lavender syrup and lemon juice. Shake for 15 seconds.
Strain the mixture into a champagne flute and top with chilled prosecco.
Finally, garnish with a fresh lavender sprig.
Notes
The lavender syrup keeps for up to 2 weeks in the refrigerator.Use only culinary lavender, as ornamental varieties can taste bitter.For a non-alcoholic version, replace prosecco with sparkling water.Keep prosecco chilled until ready to use for the best bubbles.