Million Dollar Spaghetti Casserole

Ingredients

• 16 oz. dry spaghetti
• 2 T. olive oil
• 1 c. yellow onion, from a medium yellow onion, chopped
• 4 cloves garlic, minced
• 1 1/2 lb. sweet Italian sausage, casings removed (or favorite sausage)
• 6 c. homemade marinara sauce, divided or 48 oz. jarred marinara sauce
• 8 oz. cottage or ricotta cheese
• 8 oz. cream cheese
• 1/4 c. sour cream
• 3 t. dried Italian seasoning
• 3 c. shredded mozzarella cheese, divided
• salt
• black pepper
• 1/2 c. butter, cut into slices, divided
• chopped parsley, for garnish