Preheat oven to 450 degrees F. Prepare pastry. On a lightly floured surface, roll dough from center to edges, forming a circle about 13 inches in diameter. Transfer to a 10-inch tart or quiche pan. Ease pastry into pan, being careful not to stretch pastry. Press edges of pastry against edges of pan. Trim excess pastry. Line pastry with a double thickness of heavy foil; press down firmly but carefully.
Bake pastry for 5 minutes. Remove foil. Continue baking for 7 to 9 minutes more or until pastry is nearly done (pastry will not be brown). Transfer pastry to a wire rack. Reduce oven temperature to 325 degrees F.
Meanwhile, cover dried tomatoes with boiling water; let stand for 2 minutes. Drain tomatoes well; set aside. In a small skillet cook onion in hot butter over medium heat until onion is tender.
For filling, in a large bowl stir together half-and-half and eggs. Stir in cheese, basil, salt, and pepper. Add onion mixture; mix thoroughly. Pour filling evenly into prebaked crust. Sprinkle tomatoes on top.
Bake for 30 to 35 minutes or until top of tart is golden and a knife inserted near the center comes out clean. Cut tart into 2-inch squares and serve warm. Makes 18 appetizers.