Cut two passion fruits in half. Scoop our insides of 3 halves into a cocktail shaker. Save the 4th half for garnish.
Add the vodka, passoa liqueur, simple syrup, and vanilla extract to the shaker.
Fill with ice and shake extremely vigorously. You want to create a nice foam layer when you pour.
Use a fine strainer to pour into your glass. Gently float the 4th half of passion fruit in the glass, cut side up.
Pour a small glass with champagne.
Alternate sips between glasses.