Method
1. Heat olive oil in a clean medium cast iron skillet
2. Add onion, celery stalk and carrot
3. Fry until softened - 5 min
4. Add light brown sugar, apple cider vinegar, fish stock, bay leaves and cloves to the stock mixture
5. Season with salt & pepper
6. Bring to boil
7. Arrange fresh beet in a clean slow cooker bowl
8. Top with apple
9. Add mackerel to the slow cooker bowl
10. Pour stock mixture into slow cooker bowl and cover
11. Cook in slow cooker until flaky - 1½ hr, high heat
12. Add wholegrain mustard, sour cream, fresh chives and salt & pepper to a clean small bowl
13. Mix with tablespoon
14. Transfer fish, vegetables & some of the stock to bowls, garnish with chives
15. Serve with spoonfuls of the mustard cream and crusty sliced bread