In a medium bowl, combine the sliced strawberries and granulated sugar. Toss gently and let sit for about 10 minutes to allow the strawberries to release their juices.
In a separate bowl, whip the heavy cream with the vanilla extract until soft peaks form. Be careful not to overwhip.
In a cocktail shaker, combine the vodka, lemon juice, and the macerated strawberries (including the juices). Fill the shaker with ice and shake well for about 15 seconds.
Strain the mixture into a chilled glass, filling it about halfway.
Gently spoon the whipped cream over the top of the cocktail.
Garnish with fresh mint leaves and serve immediately.