Put each haddock fillet on a piece of aluminium foil or greaseproof paper. Top with a piece of butter and season with freshly ground black pepper and lemon juice. Bring the edges of the greaseproof paper together and fold to form a sealed parcel.
Repeat the process with the remaining haddock, butter, freshly ground black pepper and lemon juice. Transfer the parcels to a baking tray and bake in the oven for 15 minutes.
Heat the oil and butter in a heavy-based frying pan and fry the black pudding for 2-3 minutes, or until crisp on the outside.
Cook the cauliflower in boiling water until tender. Drain and place the cauliflower into a food processor with some of the vegetable stock. Blend until smooth. (You may need to add all of the stock.) Add the mustard and cream and season with salt and pepper.
Spoon some of the purée onto a plate, place the pudding on top and top with the fish. Garnish with a few snipped chives.