Butter the inside and the rim of 2½ to 4 inch custard or muffin cups.
Place 1 sheet of phyllo on a sheet of wax paper. Brush it with butter. Cover with a second sheet of phyllo. Brush this layer with butter as well. Repeat with 2 more sheets of phyllo, ending with a layer of butter. Cut the stack of phyllo sheets into 4 x 4.5 inch squares.
Place one square into a muffin cup, easing it in with the backs of your fingers so that it covers half the bottom and hangs over the side of the cup.Ease in a second stack, slightly overlapping the first to cover the other half of the muffin cup.Repeat the steps to make more phyllo cups.
Bake for 10 minutes or until browned and crisp or follow the cooking instructions on the product packaging. Carefully remove tart shells from muffin cups. Let them cool completely for about 30 minutes.
In a bowl whisk together mascarpone, cream, fresh lemon zest, vanilla, and sugar or sweeteners of your choice until the mixture holds stiff peaks. Spoon mixture into shells, spreading evenly.
Mound berries and mint decoratively on mascarpone cream. Serve at once or chill up to 3 hours before serving.