In a cocktail shaker, combine 2 ounces of gin, fresh lemon juice, egg white, and lavender simple syrup and shake vigorously without ice. Add 3-4 ice cubes and shake Shake vigorously for about 15-20 seconds to chill the ingredients and mix the flavors.
Strain the cocktail mixture from the shaker into the glass, allowing it to fill about three-quarters of the way. Top it off with soda water for a refreshing fizz. You can adjust the amount of soda water based on your preference for effervescence.
Garnish with a fresh lavender sprig and a slice of lemon for an elegant touch.