1. Combine flour, sugar, and salt in processor; blend for five seconds. Add margarine; using on/off turns, blend until mixture resembles coarse meal.
2. Add two tablespoons cream and yolk. Blend until moist clumps form, adding more cream by teaspoonfuls if dough is dry.
3. Gather dough into ball; flatten into disk. Wrap and chill one hour.
4. Roll out dough on lightly floured surface to 13-inch round. Transfer dough to nine-inch-diameter tart pan with removable bottom. Trim overhang to half an inch. Fold overhang in and press firmly, forming double-thick sides. Pierce crust all over with fork; refrigerate one hour.
5. Preheat oven to 400 degrees Fahrenheit. Bake crust until golden, pressing with back of fork if crust bubbles, about 20 minutes. Cool crust completely on rack.