Bring a large pot of water to a boil and cook shells according to the packaged instructions. They should be firm (al dente) so that they hold up when filled.
Drain the noodles and transfer to a large baking sheet. Drizzle noodles with olive oil and carefully separate any stuck together noodles. Allow to cool.
Preheat oven to 350 degrees.
Make the filling by combining ricotta cheese, 1 cup pumpkin puree, parmesan, egg, nutmeg, salt, pepper, garlic, and fresh sage. Mix until combined and smooth.
In a separate bowl combine jarred sauce, the remaining pumpkin puree, and ¼ cup cream. Mix until smooth.
In a large 9x13 baking dish, spread ¾ of the sauce mixture.
Fill cooled shells with the pumpkin-ricotta filling using a spoon. You will fit about 2 Tablespoons in each shell.
Place shells, filling side up on top of the marinara. Cover baking dish with foil and bake at 350 degrees for 30 minutes.
Remove foil and sprinkle each shell with a bit of mozzarella cheese.
Place back into the oven uncovered and bake for 15 minutes until the cheese is melted and golden.
Optional: you can place under the broiler for a few seconds to brown up the cheese even more if desired!
Serve hot.
