The mousse can be refrigerated for up to 3 days before serving.
Whisk the egg yolks, sugar, and milk in a saucepan. Stir with a wooden spoon over low heat until slightly thickened, but do not boil. Remove from the heat.
Purèe the berries in a blender. Strain through a wire sieve into a large bowl to remove the seeds. Stir into the yolk mixture.
Sprinkle the gelatin over 2 tbsp of cold water in a small bowl. Let stand 5 minutes, or until spongy. Place in a shallow pan of barely simmering water and stir until the gelatin has dissolved. Remove from the heat and let cool until tepid.
Slowly stir the gelatin into the berry mixture. Beat the egg whites until soft peaks form. Whip the cream in a chilled bowl until soft peaks form. Fold the whipped cream, then the egg whites, into the fruit mixture. Divide among the dessert glasses and cover with plastic wrap.
Refrigerate for at least 4 hours or until set. Serve chilled.