method
1. Put the Bloater fillets into a bowl, cover with boiling water and leave for 20 minutes.
2. Drain Bloater fillets, rinse and dry on kitchen paper. Peel onion and cut into thin rings. Slice gherkins.
3. Drain and chop the roes and put into a bowl with the mustard. Beat to a smooth paste with a wooden spoon. Gradually trickle in all but 2 tbsp of the oil, beating well after each addition. Add pepper to taste.
4. Spread roe sauce over bottom of a serving dish and arrange Bloater fillets on top. Brush with remaining oil and decorate with onion rings and gherkins. Chill for at least 30 minutes, then serve with potato and beet salads garnished with snipped chives.
