In a mixing bowl, combine all the berries with the sugar and lemon juice. With a fork, lightly mash 1/4 of the berries against the side of the bowl. Allow the berries to sit for 1 hour. Using an electric mixer, whip the cream until stiff peaks form. In a mixing bowl, fold half of the whipped cream into the Mascarpone cheese, along with the powdered sugar. Blend until the cream is fully incorporated. To assemble, lay one layer of the sponge cake on the bottom of the pan. Brush the layer with the Pomegranate Juice. Spread 1/3 of the cheese mixture over the sponge cake. Spread a 1/3 of the berry mixture over the cheese. Repeat the procedure until all of the cake, berry and cheese mixture are used. Spread the reserved whipped cream over the top of the cake. Allow the cake to set, about 1 hour. Place a slice of the tiramisu on the plate. Garnish with raspberry (if desired), fresh mint and powdered sugar.