Place 25 ml of the lavender simple syrup* and remaining ingredients (except club soda) in a cocktail shaker with ice and shake vigorously. Strain into a glass and add club soda to taste. Garnish with a lavender sprig. Just for fun, dip the tip of a fork into a drop of blue food colouring and then into the drink to colour it slightly.
*Lavender simple syrup: Combine water and dried lavender in a saucepan. Bring to a boil, strain, and cool.