Melt the butter and lemon juice in a large oven proof dish. Place the chicken fillets in a single layer in the dish and turn to coat all over with the butter and juice. Cover with greaseproof paper, then aluminium foil, and prick holes in the foil in a few places. Bake at 350° for about 15 minutes or until chicken is tender and cooked. Remove chicken, pat dry on kitchen paper, arrange on serving dish. Cover with greaseproof paper and plastic wrap, refrigerate while preparing the mayonnaise.

Heat oil in a frypan, add onion, cook until transparent, add curry powder and cook for 2 minutes. Add the tomato sauce and wine, simmer uncovered until reduced by about half. Add the jam, stir until melted, cool, then press mixture through a large sieve or blend in a food processor until smooth. Transfer the sieved/blended mixture to a bowl and stir in the mayonnaise a batch at a time, until smooth, taste-testing between batches. Add more mayonnaise or, if preferred, some sour cream, according to individual taste.