Vanilla Syrup: In a small saucepan, combine the sugar, water, vanilla bean, and scraped seeds. Bring to a boil over medium-high heat and cook, stirring frequently, until sugar dissolves. Cool to room temperature and remove the vanilla bean.
Cocktail: Add 1 ounce of bourbon, ½ tsp Cointreau, and 2 tbsp vanilla bean syrup to a champagne flute. Fill with Prosecco and serve.