Preheat the oven to 400º. Spread the rounds of baguette on a cookie sheet and bake until golden brown. Set aside. Heat the butter in a large saucepan until melted. Add the onions and cook over medium heat and constantly stir. When the onions are golden add the flour. Mix well and lower the heat. Make sure the onions are not turning too brown. Add the wine and cook for 2 minutes over medium heat. Add the beef stock and stir until it boils rapidly. Taste to season. Let it boil for another 8 to 10 minutes. In a soup terrine drop the bread and sprinkle with the cheese on top. Ladle the soup over it. Cover with another baguette round topped with more cheese. Put the soup terrine under the broil until the cheese melts. If you do not want to keep the onion in the soup, strain them or with an hand held blender break them down.