Begin by blending 2 cups of fresh blackberries, ¼ cup granulated sugar, and 1 tablespoon of freshly squeezed lemon juice in a blender until smooth, about 1-2 minutes. Strain the mixture through a fine-mesh sieve into a bowl to remove the seeds, leaving a smooth purée. Set aside.

In a small bowl, sprinkle 1 tablespoon of gelatin powder over 3 tablespoons of cold water. Allow it to bloom for 5 minutes. Heat gently in the microwave for about 15-20 seconds to dissolve the gelatin completely, then let it cool slightly.

Once the gelatin has cooled, slowly stir it into the blackberry purée until fully combined.

In a large bowl, whip 1 cup of heavy whipping cream with 1 teaspoon of vanilla extract and a pinch of salt until stiff peaks form, about 3-5 minutes.

Gently fold the blackberry mixture into the whipped cream, starting with a small amount to lighten it, then gradually fold in the rest.

Spoon the mousse mixture into serving dishes, filling them about three-quarters full. Cover with plastic wrap and refrigerate for at least 1 hour to set.

Before serving, top each portion with extra blackberries or a dollop of whipped cream.