Add all ingredients except sparkling wine and garnish to a cocktail shaker. Shake over ice. Strain into a champagne flute.
Top with sparkling wine. Garnish with grapefruit twist.
Combine honey and boiling water in a heatproof glass jar. Stir until honey is dissolved. Cool to room temperature before using. Honey syrup will keep refrigerated in an airtight container for 2 weeks.