In large saucepan, melt butter. Sauté onions over medium heat until tender. Stir in water and bouillon mix. Bring to a boil over medium-high heat. Reduce heat, cover and simmer 15 minutes.
In a bowl, gradually stir milk into flour until smooth. Add to saucepan. Cook and stir over medium heat until mixture boils and thickens. Remove from heat, and add 3/4 cup (175 mL) of the Swiss cheese and stir until cheese is melt. Season with salt and pepper to taste.

Ladle into ovenproof soup bowls and sprinkle buttered croutons. Top with remaining Swiss cheese. Broil until cheese is melted and serve.

Buttered croutons: Toss 1 1/2 cups (375 mL) bread cubes in 3 tbsp (45 mL) melted butter. Bake in 350 °F (180 °C) oven 7 minutes. Turn cubes over and bake 7 minutes longer. Makes about 1 1/2 cups (375 mL).