Prepare your garnish by using a vegetable peeler to peel a section of lemon rind. Use a knife to clean up the edges and to cut a slit in the middle if you want to add it to the rim of your serving glass. Set aside.
Add the lemon juice, lavender syrup, vodka and lavender bitters to a cocktail shaker.
Fill the cocktail shaker with ice and give everything about 15 to 20 hard shakes.
Fill your serving glass with ice and strain the liquid into the glass.
Add seltzer to your serving glass.
Add the prepared lemon peel to the rim of your serving glass (or twist and put it inside the drink).
Optionally spray the hydrosol over top of the drink 1 to 2 times, and serve immediately.
Notes
Full instructions for making lavender syrup are on my Lavender Syrup recipe post, or you can use store bought syrup.