Prepare Pastry for Single-Crust Pie. On a lightly floured surface, roll pastry into a circle about 12 inches in diameter. Transfer to a 10-inch tart pan; ease pastry into pan. Trim pastry even with rim of pan. Do not prick pastry. Line pastry shell with a double thickness of foil. Bake pastry in a 450 degree F oven for 5 minutes. Remove foil. Bake for 5 to 7 minutes more or until pastry is set and dry. Remove from oven. Reduce oven temperature to 325 degrees F. Sprinkle tart shell with Parmesan cheese.
Meanwhile, in a small mixing bowl beat egg whites slightly. Stir in ricotta cheese, garlic, and the 1 tablespoon thyme; spread over pastry.
Overlap large tomato slices in a circle around edge. Arrange yellow cherry tomato slices in a circle within the tomato ring. Fill center with red cherry tomato slices. Stir together olive oil or cooking oil and the 2 teaspoons thyme. Brush tomatoes with oil mixture.
Bake tart in a 325 degree F oven for 25 to 30 minutes or until heated through and nearly set. Serve warm or at room temperature. Refrigerate any leftover tart. Makes 10 to 12 appetizer servings.
Pastry for Single-Crust Pie
In a large mixing bowl stir together all-purpose flour and salt. Using a pastry blender, cut in shortening until pieces are pea size. Sprinkle 1 tablespoon cold water over part of the mixture; gently toss with a fork. Push moistened dough to the side of the bowl. Repeat moistening dough, using 1 tablespoon cold water at a time, until all the dough is moistened. Form dough into a ball.