01 - Combine berries, sugar, and 1 cup water in a saucepan. Bring to a simmer and cook for 5 minutes, gently mashing berries with a spoon to release juices.
02 - Pour the cooked berry mixture through a fine mesh sieve to remove seeds and pulp. Return the strained liquid to the saucepan.
03 - Sprinkle gelatin envelopes over 1/2 cup cold water in a small bowl. Let stand for 5 minutes until softened and bloomed.
04 - Stir the bloomed gelatin into the hot berry liquid until completely dissolved. Add lemon juice and mix thoroughly.
05 - Pour the berry mixture into serving glasses or a trifle dish, filling about halfway. Refrigerate for at least 2 hours until firmly set.
06 - Split vanilla bean lengthwise and scrape seeds into a saucepan. Add milk and heat just until steaming. Remove from heat.
07 - Whisk egg yolks with sugar until pale and thickened. Slowly pour hot milk mixture into yolks while whisking constantly to prevent curdling.
08 - Return mixture to saucepan and cook over low heat, stirring constantly, until slightly thickened and coating the back of a spoon. Do not boil.
09 - Sprinkle gelatin powder over 1 tablespoon cold water. Let stand for 5 minutes, then stir into warm custard until dissolved.
10 - Let custard cool to room temperature, stirring occasionally to prevent skin formation on surface.
11 - Beat cold heavy cream with electric mixer until soft peaks form. Do not overbeat.
12 - Gently fold whipped cream into cooled custard until fully incorporated and smooth, maintaining light texture.
13 - Once berry jello is completely set, spoon or pipe vanilla mousse over the jello layer in each serving glass.
14 - Refrigerate for at least 2 additional hours until mousse layer is firm and completely set.
15 - Top with fresh berries and mint leaves immediately before serving. Serve chilled.