Melt butter in a skillet over medium heat. Add onion and garlic and cook, stirring, until onion is soft. Reduce heat to low, add Camembert, and stir until soft; remove from heat. In a small bowl, beat together egg, ricotta, parsley and 1/4 cup of the Parmesan; stir into Camembert mixture.

Following package directions, cook pasta shells until al dente. Drain, rinse under cold running water, and drain again. Stuff shells with cheese filling.

Spread half the spaghetti sauce in a 7 x 11 inch baking dish or shallow 2 1/2 qt casserole. Arrange shells, filling side up, in sauce. Spoon remaining sauce in a band over top of each. Bake, covered, at 350 F until hot and bubbly, about 30 minutes. Sprinkle with remaining 1/4 cup Parmesan.