Simple Syrup: in a small saucepan, whisk together sugar, water, and lavender flowers. Bring to a simmer to allow sugar to dissolve in the water; continue to simmer for 1-2 minutes. Remove from heat and let infuse for 10 minutes. Store in an airtight container in the fridge if not using immediately.
Cocktail: in a Champagne flute, add chilled vodka, lemon juice, and lavender simple syrup. Top with Champagne or prosecco and garnish with lemon peel as desired.
If your ingredients are not chilled, you can add the vodka, lemon juice, and lavender simple syrup to an iced cocktail shaker. Stir gently, pour into a champagne flute, and top with the champagne.