Puree strawberries. You should have about 1 cup of strawberry puree when finished. Sprinkle gelatin on top and pulse to combine. Continue pulsing a few times every 3-4 minutes while you prepare the rest of the mousse.
Whip heavy cream until strong peaks form. Add in vanilla and sugar. Mix again to combine. Add in sour cream and repeat.
Pour strawberry puree in with cream mixture and mix for about 3 minutes. Mousse should be soft, light and hold soft peaks. Serve immediately or transfer to a piping bag and store in the fridge until ready to serve. Pipe into small bowls and top with a strawberry to serve. I think it's also lovely with chocolate shavings on top!