In a large bowl whip the heavy cream until stiff peaks form.
Add 1/2 cup confectioners' sugar and mix until well blended.
In a medium bowl mix mascarpone cheese with vanilla extract and other 1/2 cup sugar.
Fold in whipped cream.
In a medium bowl, puree thawed mixed berries with granulated sugar. Microwave for 1-2 minutes if necessary.
Separate lady fingers and dip each one (flat side down) in the berry puree.
Arrange in concentric circles on the bottom of the trifle bowl. Stack ladyfingers up along the sides of the trifle bowl so they are visible from the outside. This will create a cake "crust" for the filling.
Drizzle berry puree over the ladyfingers on the bottom.
Spread mascarpone/cream mixture over ladyfingers.
Add strawberries and blackberries. Continue layers of cream, berries, and puree.
In center layer, add more ladyfingers.
Continue layers of mascarpone/cream, berries, and puree until the top of trifle bowl.
Arrange strawberry slices along the edge of the the trifle bowl. Arrange raspberries and blackberries in concentric circles on the top layer of cream. Cover and refrigerate for 2 hours.
Reserve remaining puree for guests to drizzle over individual servings.