Place the onion and cabbage in a lidded saucepan, cover with water, add the salt, juniper, caraway seeds and vinegar and bring to the boil. Reduce to a simmer, cover with a lid and cook for 30–40 minutes.
Put the fish on a plate and dust with the curry powder, turning to make sure it is well coated.
Heat the butter and oil in a frying pan over a medium–high heat, add the garlic clove and cook the fish for 5–10 minutes or until cooked through, basting with the butter and oil.
To serve, divide the cabbage between two plates, top with the fish, decorate with some apple and drizzle over the fragrant butter.