Heat the butter and oil in a large pan and cook the onions slowly until deep gold and soft – about 10-20 minutes – stirring every now and then.
Add the carrots, celery, garlic and potatoes and cook for a couple of minutes. Add the bay leaves, stock and ale and bring to the boil. Simmer for about 15-20 minutes or until the vegetables are tender.
Liquidise in a blender and return to the pan. Add the cheese, mustard, pepper and Worcestershire sauce and a little salt and pepper. You may want more of any of them. Serve piping hot with the bread.
This soup is very rich and indulgent, so shouldn't be eaten too often. But it's perfect for those special occasions!
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