Heat the oven to 350 degrees F. Lightly grease a 9x13-inch baking dish.
Bring a large pot of salted water to a boil over high heat and boil the pasta until al dente according to package directions.
Meanwhile, in a medium bowl, whisk the eggs, parsley and Parmesan. Drain the spaghetti, and add it right back to the hot pot. Add the butter and the egg mixture to the spaghetti, and quickly toss until evenly coated and the eggs have formed a sauce. Add the cottage cheese and cream cheese and toss until combined. Transfer the mixture to the baking dish.
Heat a large skillet over medium heat. Add the sausage and brown all over, about 5 to 8 minutes. Remove from the heat, and stir in the marinara sauce. Spread mixture over the spaghetti. Add the mozzarella cheese in an even layer over top.
Transfer the baking dish to the oven and bake 30 to 45 minutes or until the cheese has melted and is lightly browned on top. Cool 5 minutes before serving. Serve with parmesan and basil, if desired.