Bring a large pot of salted water to the boil and preheat the oven to 200C/350F. Once water is boiling, add the shells and cook 9-10 minutes until almost al dente. Drain and run under cold water to make cool enough to handle.
Combine cottage cheese, 3 tablespoons parmesan, chopped chives, italian seasoning and salt and pepper in a small bowl.
Spread about half of the marinara over the bottom of an oven dish, skillet or oven-proof pasta plate.
Stuff each of the shells with about a teaspoon of the cheese mixture and arrange over the marinara. Cover with tin foil and bake 20 minutes.
To make the alfredo sauce: bring the milk and crushed garlic to a simmer in a small saucepan, once it is almost bubbling, add the cornstarch mixed into 1tsp of water, the cheeses and a grind or two of black pepper. Allow to gently simmer until thickened slightly.
Pour the alfredo mixture over the shells, followed by a few dollops of the marinara sauce. Top with the breadcrumbs and the shredded mozzarella. Broil until the top is golden brown.
Serve on its own or with a garden salad.