Prepare the Raspberry Puree

1. Make the Raspberry Puree: In a blender or food processor, blend the raspberries until smooth. Strain the mixture through a fine sieve to remove the seeds, pressing the berries with the back of a spoon to get as much juice as possible.
2. Sweeten the Puree: Stir in 1/4 cup powdered sugar into the raspberry puree, adjusting sweetness to your preference. Set aside.

Prepare the Gelatin

1. Bloom the Gelatin: In a small bowl, sprinkle the gelatin over the 3 tablespoons of water. Let it sit for about 5 minutes to bloom. This process allows the gelatin to dissolve evenly.
2. Dissolve the Gelatin: After 5 minutes, heat the gelatin mixture in the microwave for about 15 seconds, or until completely dissolved. Set it aside.

Make the Mousse Base

1. Whip the Cream: In a separate bowl, whip the heavy cream until stiff peaks form. Be careful not to overwhip.
2. Mix in Sour Cream/Yogurt: Gently fold in the sour cream or Greek yogurt into the whipped cream, combining them until smooth.
3. Add the Raspberry Puree: Slowly fold the sweetened raspberry puree into the whipped cream mixture until well combined.
4. Add the Gelatin: Stir in the dissolved gelatin mixture into the raspberry mixture, ensuring it’s fully incorporated.

Chill the Mousse

1. Fold in Whipped Cream: Carefully fold in the whipped cream to add air and lightness to the mousse, keeping its fluffy texture.
2. Chill the Mousse: Spoon the mousse into individual serving glasses or bowls, cover with plastic wrap, and refrigerate for at least 4 hours, or overnight if you prefer.