Gently stir the raspberries, blueberries, and strawberries in a bowl with the granulated sugar, 2 tablespoons of the Chambord, and 1/2 cup of the raspberry coulis. Whip the heavy cream in a large bowl with an electric mixer on high speed or a whisk until it thickens and almost doubles in volume. Add 1/4 cup of the confectioners' sugar and 1 tablespoon of the Chambord and whip until stiff peaks form. In a medium bowl, whip the mascarpone with the remaining 1/4 cup confectioners' sugar with an electric mixer on low speed until smooth. Fold in half of the whipped cream. Spread half the pound cake slices in the bottom of a deep 6 x 9-inch pan. Drizzle the remaining 1/4 cup Chambord over the cake and cover with half of the berry mixture. Cover the berries with half of the mascarpone cream, gently spreading it into a smooth layer with a rubber spatula. Repeat with the remaining ingredients and top with a smooth layer of the remaining whipped cream. Cover tightly with plastic wrap. Refrigerate for at least 2 hours, and up to 1 1/2 days. Spoon into bowls and garnish with the mint sprigs. Serve with the remaining raspberry coulis spooned over each serving or passed on the side.
Yield: 6 to 8 servings