Preheat the oven to 350°F (175°C).
Prepare the 12 jumbo pasta shells according to the cooking directions provided on the package. Once cooked, drain and set them aside until cool enough to handle comfortably.
Place the cottage cheese, 1 cup shredded mozzarella, grated Parmesan, egg, minced parsley, onion powder, garlic powder, Italian seasoning, salt, and black pepper in a mixing bowl. Stir gently until the cheeses, egg, herbs, and seasonings are evenly incorporated.
Spread 1 cup of the pasta sauce evenly across the bottom of an 8 × 8-inch casserole dish.
Fill each cooled pasta shell with approximately 2 tablespoons of the cottage cheese mixture. Position the filled shells in a single layer over the sauce in the baking dish.
Spoon the remaining 1 cup of pasta sauce over the arranged shells, distributing it evenly across the surface.
Scatter the reserved ½ cup of shredded mozzarella over the sauce-covered shells. Loosely cover the casserole dish with aluminum foil to help prevent the cheese from becoming overly browned during the initial baking period.
Bake the covered stuffed shells for 20–25 minutes, or until the casserole is thoroughly heated and the sauce is bubbling.
Remove the foil and return the dish to the oven for another 3–5 minutes, allowing the mozzarella topping to melt completely and develop a lightly golden finish.
Remove the casserole from the oven and allow the stuffed shells to rest for approximately 10 minutes before serving.