In a medium bowl, sprinkle the strawberries with the sugar and mash lightly with a fork until the strawberries have exuded some juice and the sugar begins to dissolve. Let macerate for 15 minutes.
Strain the juice from the strawberries into a bowl. Whisk the sour cream into the juice. In a medium bowl, whip the heavy cream to soft peaks. Fold in the sour cream mixture. Gently fold in the strawberries. Refrigerate until chilled, at least 20 minutes. Spoon the mousse into bowls and garnish with the mint.