Make the lavender syrup first. Combine water and sugar in a small saucepan over medium heat. Stir until the sugar dissolves.
Add dried lavender to the syrup mixture. Remove the saucepan from heat and let the mixture steep for 10 minutes.
Strain the syrup through a fine mesh strainer. Let it cool to room temperature.
Fill a cocktail shaker with ice. Add lavender syrup and fresh lemon juice.
Shake for 15 seconds until well chilled.
Strain the mixture into a champagne flute.
Top the drink with chilled prosecco.
Garnish with a lemon twist or lavender sprig.
Notes
The lavender syrup stays fresh in the refrigerator for up to 2 weeks in an airtight container.Make a non-alcoholic version by replacing prosecco with sparkling water or lemon-lime soda.For a stronger lavender flavor, steep the dried flowers for up to 15 minutes.Chill glasses in the freezer for 10 minutes before serving for the best results.