To prepare cream: Stir together water and gelatin in a small heatproof cup or bowl. Microwave, uncovered, on High until the gelatin has completely dissolved but the liquid is not boiling, 20 to 30 seconds. (Alternatively, bring 1/2 inch water to a gentle simmer in a small skillet. Set the bowl with the gelatin mixture in the simmering water until the gelatin has dissolved completely.) Stir the mixture until smooth.

Place strawberries, sugar and vanilla in a food processor and puree. Add sour cream; pulse to combine. With the motor running, slowly add the dissolved gelatin. Pour the cream into four 8-ounce bowls or wineglasses. Cover and refrigerate until set, about 3 hours.

To prepare topping & serve: Toss diced strawberries and sugar in a small bowl; let stand until slightly juicy, about 2 minutes. Divide among the creams.

MAKE AHEAD TIP: Prepare through Step 2, cover and refrigerate for up to 3 days. Add topping just before serving.