Melt the Stork Margarine in a large heavy-bottomed saucepan. Add the onions and fry with the lid on for 6-8 minutes until softened. Sprinkle in the sugar and cook for 10-12 minutes more on low heat, stirring frequently, until caramelised. Take care not to let the onions blacken or burn while cooking.
Add the garlic to the pan and cook for further 3 minutes on low heat. Sprinkle in the flour and stir well. Increase the heat and keep stirring as you gradually add the hot Knorr Beef Stock. Reduce heat, cover and simmer for 15-20 minutes.
Meanwhile, toast the French bread under the grill, then set aside, but leave the grill on.
To serve, ladle the soup into heatproof bowls and put a slice or two of toasted bread on top, then sprinkle on the cheese. Grill until the cheese has just melted before serving.