In a small bowl, mix the gelatin in warm water until dissolved. In a 2-quart saucepan, mix the half-and-half and sugar. Heat until bubbles form around the edge (do not boil). Remove from the heat. Beat in the gelatin and vanilla with a wire whisk until smooth. Place the sour cream in a large bowl. Gradually whisk in the warm gelatin mixture until smooth. Pour into 8 (6 ounce) custard cups. Cover loosely. Refrigerate for 4 hours or until completely set. Meanwhile, place the frozen strawberries in food processor. Cover and process for 30 seconds or until pureed. Press through a fine mesh strainer to remove the seeds. You should have around 1/2 cup of juice and puree. In a 1-quart saucepan, mix 1 tablespoon water and cornstarch until smooth. Stir in the strawberry puree. Cook over medium heat until the mixture boils. Boil for 1 minute. Set aside to cool. Cover loosely and refrigerate until serving time. To serve, run the tip of a knife around the edge of each custard cup to loosen the panna cotta. Tip each onto a dessert dish and shake to unmold. Drizzle with the strawberry sauce and top with the fresh berries.