Place martini glasses in the freezer for 15 minutes to chill (or fill with ice water for a few minutes). Muddle 3-4 mint leaves in the bottom of a cocktail shaker. Add ice, vodka, pomegranate juice and 1/2 of the champagne. Shake a few times but be careful – too many shakes will make the top explode! Strain into chilled martini glass, top with remaining champagne and garnish with a pinch of mint.