Oyster Soup au Gratin (For Christmas Oyster Leftovers) | RICARDO

Ingredients

• 4 cups (1 litre) thinly sliced onion
• 8 oz (227 g) white button mushrooms, quartered
• 3 tablespoons (45 ml) butter
• 2 tablespoons (30 ml) flour
• 4 cups (1 litre) chicken broth
• 2 cups (500 ml) oysters, with their juice
• 6 slices country bread, toasted or not
• 2 cups (500 ml) Swiss cheese, grated
• Salt and pepper