Heat oil and butter in a large saucepan over medium heat.
onions and cook, stirring frequently, 30 minutes or until
softened and caramelized. Stir in flour to coat onions.
Cook 1 minute. Slowly stir in broth. Cover; cook over
low heat 20 minutes. Add sherry.
Heat broiler. Spoon soup into 6 individual oven-proof bowls.
Top each with a slice of bread and a slice of cheese. Broil
briefly to melt cheese and serve.