Puree the strawberries in a food processor, then strain to remove seeds.
Whisk icing sugar and vinegar into strawberries.
Whip the whipping cream until soft peaks form.
Fold in sour cream.
Add additional sugar at this point if it is not sweet enough.
Spoon mixture into 4 ramekins and cover with saran wrap, and freeze.
To serve: remove from freezer about 1 1/2 hours before serving.
Garnish each dish with an additional strawberry.
**Note:You can also make a facsimile of crème fraîche by adding a tablespoon of buttermilk or a half cup of sour cream to a cup of whipping cream, heating it gently to 110°F (45°C), then putting it in a loosely covered bottle in a warm place and letting it sit for anywhere from 8 hours to a couple of days, until thick. Store it in the refrigerator, where it will thicken further, and keep for about three weeks. In general, crème fraîche and sour cream can be used interchangeably in most recipes, but crème fraîche has two advantages over sour cream: it can be whipped like whipping cream, and it will not curdle if boiled**.