Preheat the oven to 400 degrees . Arrange the puff pastry on a baking sheet and bake until golden, about 15 minutes. Let cool on a rack for 5 minutes; split each piece into 2 layers.
In a large bowl, combine the berries. In a large, nonreactive skillet, combine 3 cups berries, 1/4 cup sugar, the lemon juice and port over medium heat. Bring to a simmer and cook until thickened, about 8 minutes. Transfer to a bowl and refrigerate until cool.
Using an electric mixer, beat the heavy cream, mascarpone, vanilla and the remaining 3 tablespoons sugar until stiff, about 2 minutes. Fold in 3/4 cup berry compote.
Spread the remaining berry compote on the pastry bottoms. Top them with some berry cream, the remaining fresh berries and the pastry tops. Dollop with the remaining berry cream before serving.