Preheat the oven to 350 degrees F. Lightly grease a
9 or 10-inch fluted, false bottom, tart pan (available at cookware stores). For the pastry, combine sugar and flour in a bowl. Mix in the butter with a fork until the mixture resembles a pea-sized crumble. Add the water and gently mix until mixture just holds together when squeezed, but is still quite crumbly. Spoon the mixture into the pan. With lightly floured hands, firmly press the dough evenly into the tart pan, then refrigerate 30 minutes.
Combine filling ingredients in a bowl and pour into tart shell. Bake for 30 minutes, or until filling is set and crust is cooked. Cool tart on a rack to room temperature. Remove the tart pan's outer ring, then refrigerate tart until nicely set. Cut into portions. If desired, dust with icing sugar and garnish each slice with a fresh mint sprig.