Ingredients:

6 tablespoons butter
3 large onions, thinly sliced
2 potatoes, thinly sliced
4 cups fresh or canned beef stock or broth 
2 cups water
3 cups heavy cream
Salt
Freshly ground black pepper
2 to 3 cups grated Parmesan and Swiss cheeses, mixed together

Preparation:

Melt the butter in a large casserole or pot. 
Add the onions and cook over medium heat, stirring, 
until brown and caramel colored, about 15 minutes.
Add the potatoes, stock, and water.
Cover and bring to a boil. 
Reduce the heat to low and simmer until the potatoes are tender, about 45 minutes.
Add the cream and reheat. Season to taste with salt and pepper. 
Top with the cheeses.