Preheat oven to 400 degrees F (200 degrees C).

Grease a 9x13-inch baking dish.

Fill a large pot with lightly salted water and bring to a rolling boil. Stir in spaghetti and return to a boil. Cook until pasta is tender but still slightly firm, about 10 minutes. Drain well.

Transfer spaghetti to a large bowl and toss with spaghetti sauce until well combined.

Mix cottage cheese and sour cream in a bowl.

Spread half the spaghetti with sauce into the prepared baking dish.

Spread the cottage cheese mixture evenly over the spaghetti.

Place the remaining spaghetti and sauce in an even layer over the cottage cheese mixture; sprinkle with mozzarella cheese.

Bake in the preheated oven until bubbly and the cheese is browned, 30 to 40 minutes.