Prepare piecrust according to package directions to fit into a 9-inch tart pan with a removable bottom. Bake until light golden brown. Cool completely.
Combine mascarpone and next 4 ingredients in a large bowl, beating with an electric mixer at medium speed until stiff peaks form. Spoon mixture into crust, spreading evenly.
Gently combine berries and place on filling. Release sides of pan from bottom before serving.
Note: Tart may be assembled two hours ahead and chilled. Bring to room temperature before serving.