Cook pasta according to package directions, drain & transfer to a large bowl. Stir in the sausage, soup, sauerkraut, 2 c Swiss cheese, milk, onions, mustard & garlic.
Spoon into 9 x 13 greased baking dish. Sprinkle with remaining cheese.
Bake uncovered at 350 for 45-50 minutes or until golden brown & bubbly.