In a skillet, sauté onion in butter until tender. Add tomatoes, salt, pepper and thyme. Cook over medium-high heat until liquid is almost evaporated, about 10-15 minutes. Remove from heat. Sprinkle 1 cup cheese into pastry shell. Cover with tomato mixture, sprinkle with remaining cheese. In a mixing bowl, beat eggs until foamy. Stir in cream; mix well. Pour into pastry shell. Bake at 425° for 10 minutes. Reduce heat to 325°, bake 40 minutes, or until top begins to brown and a knife inserted near the center comes out clean. Let stand 10 minutes before cutting.