Preheat oven to 350 degrees F. Lightly grease a 9x13-inch baking dish.
Cook the spaghetti to al dente as directed on package. Meanwhile, in medium bowl, whisk together the eggs, parsley and Parmesan cheese. Drain the spaghetti, and put it back to the hot pot. Add the butter and the egg mixture to the spaghetti, and quickly stir with a wooden spoon until evenly coated and the eggs have formed a sauce. Pour the spaghetti into the prepared baking dish and smooth into an even layer.
Add the cottage cheese and cream cheese to the pot (off the heat) and stir with a wooden spoon until the cream cheese is melted down and the mixture is completely combined. Pour the cream cheese mixture over the spaghetti layer in the pan, and spread it into an even layer.
Heat a medium skillet over medium heat and brown the sausage, breaking it up while it cooks, until it's no longer pink in the middle. Remove from heat, use a slotted spoon to transfer the sausage to the now-empty pot, and stir in the pasta sauce and heavy cream. Spread the mixture over the cream cheese layer.
Lay the slices of mozzarella over top of the sausage layer. Bake until the filling the bubbling and the cheese is melted and lightly browned on top, 30 to 45 minutes. Sprinkle with the basil. Allow to sit for at least 10 minutes before serving.
Make-Ahead Note: This casserole can be assembled through step #4, covered with plastic wrap, and refrigerated overnight. Let sit at room temperature while the oven preheats and then proceed with step #5.Nutritional values are based on one serving