Combine the butterfly pea flowers and vodka in a small bowl to infuse the color of the vodka. Infuse for 5-10 minutes, depending on how deep of a purple/blue color you want.
Add all of the ingredients into a cocktail shaker with ice cubes.
Shake with ice and strain into a martini glass.
Notes
You don't have to make this Halloween-themed, but I do love how festive it is!