Let piecrust stand at room temperature according to package directions. Unroll piecrust into a 9-inch pie plate. Crimp edge as desired. Line unpricked pastry with a double thickness of foil. Bake in a 425 degree F oven for 8 minutes. Remove foil. Bake for 4 to 5 minutes more or until pastry is set and dry. Remove from oven. Reduce oven temperature to 375 degrees F.
Meanwhile, place tomato slices on paper towels to absorb excess moisture. In a small skillet, melt butter over medium heat. Add onion. Cook until onion is tender but not brown, stirring occasionally.
In a medium bowl, whisk together eggs, half-and-half, flour, basil, salt, dry mustard and black pepper.
To assemble, sprinkle cheese onto bottom of the hot, baked pastry shell. Spoon onion mixture over cheese. Arrange a single layer of tomato slices over cheese, overlapping slightly. Slowly pour egg mixture over tomatoes. Sprinkle paprika over egg mixture.
Bake, uncovered, for 35 to 40 minutes or until egg mixture is set in center. If necessary, cover edge of pie with foil for the last 5 to 10 minutes of baking to prevent overbrowning. Let stand 10 minutes before serving. Makes 6 servings.