Combine equal parts sugar and water in a pan and simmer until it is an even consistency and the sugar is dissolved completely. Stir in butterfly pea flower powder to get a dark blue color. The mixture will be dark blue until the lemon hits the syrup, creating a lavender color. Add food-grade dried lavender to the mixture and let it soak until desired strength of flavor.

FOR THE COCKTAIL:

Combine vodka, lavender syrup and lemon juice in a shaker. Shake with ice. Pour mixture into a glass with ice and top with club soda. Garnish with a sprig of lavender.