In a medium saucepan, combine fresh raspberries and granulated sugar over low heat. Stir gently for 2–3 minutes until the raspberries soften and turn syrupy. Remove from heat and puree using a blender until smooth, then strain through a fine sieve into a bowl to remove seeds.

If using gelatin, sprinkle the gelatin powder over cold water in a small bowl and let it sit for 5 minutes. Gently heat the mixture until melted and smooth; allow it to cool slightly before mixing it with the cooled raspberry puree.

In a large mixing bowl, pour in the chilled heavy whipping cream and whip on medium speed until soft peaks form, about 3–5 minutes.

Gently fold the raspberry puree into the whipped cream in three additions, being careful not to deflate the whipped cream too much.

Spoon the mousse mixture into serving glasses or bowls, filling them about three-quarters full. Cover and refrigerate for at least 2 hours to set.

Once chilled, garnish each serving with fresh raspberries and mint before serving.