Before you prepare the mascarpone, let the berry sauce cool down. Place the berries, sugar, and lemon juice in a small saucepan. Heat on medium heat. Reduce heat to medium and simmer the mixture for 15 minutes, stirring now and again, until it thickens.
Take off heat, and strain to get rid of seeds.
While the sauce is being prepared, prepare the gelatin. Let the gelatin dissolve in cold water for 5-10 minutes.
Heat gelatin on low heat until it dissolves. Then, pour it over the berry sauce. Allow the berry sauce to cool at room temperature before you start making the rest.
Line a springform pan 8″ (20 cm) in diameter with parchment paper. Ladyfingers can be used to line the edges and bottom. To fill in the gaps, trim the ladyfingers if necessary.
Make berry and chocolate mousse fillings. Now Combine the cream and chocolate in a heatproof bowl. Place it over a saucepan of simmering water. Let cool on low heat.
Make the gelatin. Let gelatin dissolve in cold water for 5-10 minutes.
Let gelatin melt in a small saucepan on low heat.
Now Mix the mascarpone and powdered sugar in a large bowl until well combined. After this, Whip the whipping cream in a separate bowl until it forms stiff peaks. Next, add the whipped cream to the mascarpone mix.
Divide the mixture into two.
Combine half the mascarpone with melted chocolate, and pour it onto the bottom of a pan. Sprinkle fresh raspberries and mixed berries over the top. Allow cooling in the refrigerator for between 15 and 30 minutes.
Mix the berry mixture with half of the mascarpone mixture. It should be poured on top of the chocolate mousse.
Allow to cool for at least 6 hours, or overnight, until set.
Decorate the platter with fresh berries, mint leaves, and ribbon before serving.