Preparation

Whisk together flour, sugar, and salt in a large bowl. Blend together flour and butter with your fingertips or a pastry blender until most of mixture resembles coarse meal with small (roughly pea-size) butter lumps. Beat together yolk, vanilla, lemon juice, and water with a fork and stir into flour with fork until combined well.

Gently knead with floured hands in bowl until a dough forms. Turn dough out onto a floured surface and gently kneaded 4 or 5 times.
Form dough into a ball, then flatten into a disk and chill, wrapped in plastic wrap, at least 1 hour and up to 2 days.  Makes enough dough for a 9- to 10-inch tart.

Roll out dough with a floured rolling pin into a 13-inch round on a floured surface and fit into tart pan (if pastry breaks, press together with your fingers). Trim excess dough, leaving a ¨ö-inch overhang, then fold overhang inward and press against side of pan to reinforce edge. Lightly prick bottom of shell all over with a fork. Chill 30 minutes.

Preheat oven to 375˚F. Line shell with foil and fill with pie weights. Bake in middle of oven 10 minutes, then carefully remove foil and weights and bake shell until golden, 13 to 15 minutes more. Transfer shell in pan to rack to cool.

Make filling just before serving:
Cut peel, including all white pith, from fruit with a sharp paring knife, then cut segments free from membranes and pat dry with paper towels. Squeeze 3 tablespoons juice from membranes into a bowl. Whisk together mascarpone, candied ginger, 2 tablespoons juice, and 2 tablespoons confectioners sugar. Add remaining tablespoon juice of mixture is too thick.

Spread ginger mascarpone evenly in tart shell and top decoratively with fruit. Dust with remaining 2 tablespoons confectioners sugar and serve immediately.