Preheat oven to 400 degrees. Fry the bacon in a soup kettle. Add onions and garlic, saute until tender. Add sauerkraut, chicken stock, mustard, potatoes, caraway seeds and corned beef. Heat through. Cut bread into 1/2-inch squares, spread on a baking sheet, drizzle with butter and bake in oven for ten minutes or until crisp through. Ladle soup into bowls, sprinkle with the pumpernickel croutons and top with one teaspoon grated Swiss cheese. Makes 12 servings.