Line a 9-inch springform pan with wax paper.
Beat mascarpone cheese and sugar together in a large bowl until blended. Add the lemon juice and zest, and beat to blend well.
In a separate bowl, beat the whipping cream until stiff peaks form. Fold (gently stithe whipped cream into the mascarpone mixture, then transfer 2.5 cups to a bowl, cover and refrigerate.
Fold the cubed pound cake into the remaining mascarpone mixture. Spread half of this cake mixture into the prepared pan. Line the edge of the filling near the pan with raspberries (this will form the decorative edge.) Top the filling with 2 cups of raspberries.
Spread the remaining cake mixture in the pan on top of the raspberry layer. Line the edge of this layer with blueberries. Top the filling with 1¾ cups of blueberries.
Spread the reserved mascarpone mixture on top, and line the edge of the torte with the remaining raspberries. Then, use the remaining blueberries to make a star shape (or other decoration as preferred.)
Cover and freeze for at least 4 hours or overnight.
Prior to serving, remove torte from freezer and allow to sit at room temperature for at least 10 minutes to soften slightly. Carefully run a warm knife around the edge of the pan to loosen; remove sides of pan, and serve.