Cook ground Italian sausage and onion in a medium nonstick pan until pork is no longer pink, breaking it up with a wooden spoon.
Add garlic, salt and pepper and cook 1 minute.
Roughly chop the tomatoes and add them and any juices to the pan along with the tomato paste. Stir to combine.
Simmer until thickened.
In a medium bowl, stir together cottage cheese, egg, and Parmesan cheese.
Spread cottage cheese mixture along bottom of a 9-inch cast iron skillet or a greased baking dish.
Top with 1 cup of shredded Mozzarella cheese.
Pour tomato mixture evenly on top of cheese.
Sprinkle remaining Mozzarella cheese on top.
Place in 375 degree oven for 20 minutes.
Optional- Broil for 2 to 3 minutes to brown cheese.
Sprinkle with parsley.