Bring a large pot of lightly salted water to a boil. Cook jumbo shells in the boiling water, stirring occasionally, until tender yet firm to the bite, about 9 minutes.

Meanwhile, mix cottage cheese, ricotta cheese, 1 cup mozzarella cheese, Parmesan cheese, egg, parsley, salt, and pepper together in a large bowl.

Preheat the oven to 350 degrees F (175 degrees C).

Drain pasta shells, arrange into a baking dish, and stuff with cheese mixture. Pour tomato sauce over shells.

Bake in the preheated oven until cheeses are melted, about 45 minutes. Remove dish from oven; set an oven rack about 6 inches from the heat source and preheat the oven's broiler. Top shells with remaining mozzarella cheese and broil until cheese is melted, about 10 minutes more.