This goes brilliantly with any firm-fleshed white fish.
Melt one-third of the butter in a heavy-based pan and sauté the diced onion in it, stirring until it becomes translucent.
Add another third of the butter and stir in the flour. Cook, stirring, over a low heat for 2 minutes.
Whisk in the cider and bring quickly to a boil. Lower to a simmer, season with salt, pepper and grated nutmeg, and cook for 10 minutes.
Add the crème fraîche, raise the heat and bubble. Immediately remove from the heat and whisk in the remaining butter in little bits. Finish with the lemon juice. Don’t attempt to reheat or your beautifully coherent sauce will disintegrate.
© 1998 Alastair Little and Richard Whittington estate. All rights reserved.