01 - Heat 6 tablespoons cream in a small saucepan over low heat until just steaming. Remove from heat, add chopped chocolate, and let stand 1 minute. Stir until completely smooth and glossy.
02 - Whisk maple syrup, vanilla extract, and salt into the chocolate mixture. Set aside to cool to room temperature, stirring occasionally.
03 - In a medium bowl, whip the remaining 6 tablespoons cream until soft peaks form. Do not overwhip.
04 - Gently fold one-third of the whipped cream into the cooled chocolate base to lighten it. Fold in remaining cream until no white streaks remain. Mixture should be airy and smooth.
05 - Combine mixed berries, maple syrup, and lemon juice in a bowl. Toss gently to coat evenly.
06 - Divide half the berry mixture among four serving glasses. Top each with chocolate mousse, smoothing the surface. Layer remaining berries over the mousse.
07 - Refrigerate for at least 1 hour to set. Garnish with fresh mint leaves and shaved chocolate just before serving.