French Onion Soup

Ingredients

• 4 large onions sliced very thinly
• 4 tbsp extra-virgin olive oil or butter
• 3 1/2 cups water
• 2 tbsp plain flour or rice flour
• 4 cups vegetable stock or beef stock
• 2 tbsp port (optional)
• 1 1/2 tsp salt
• 1/2 tsp freshly ground black pepper
• 1 baguette cut into 18 slices
• 150g/5oz gruyere or cheddar cheese grated