1Heat butter in a saucepan over medium-high heat.
2Add garlic, celery, onions, peppers, and leeks, and season with salt and pepper.
3Cook, stirring, until soft, 8–10 minutes.
4Add carrots, parsnips, celeriac, potatoes, stock, milk, cream, and Worcestershire; bring to a boil. Reduce heat to medium, and cook, stirring occasionally, until vegetables are tender, about 25 minutes.
5Add cod and continue to cook, stirring gently, until fish is cooked through, 6–8 minutes.
6Stir in dill, parsley, lemon juice, and salt and pepper.
7Serve with bread.