This sauce is also very good over a grilled (broiled) chicken breast or steak. You can make as much or as little of it as you need, but I try to have at least two generous tablespoons per serving. Your fishmonger should be able to skin the fish when he guts them (and you can use different fish, if you prefer). It’s best to decide beforehand how you are going to serve the sole — you can cook them ready-filleted, or cook them whole and serve with sauce spooned over and let everyone fillet their own on their plate. They come away from the bone easily, but it’s still always worth double-checking for tiny missed bones. They do look impressive served whole — so often I serve them like that, then move the fish to a clean empty plate, quickly fillet it and return the fillets to the plate of sauce. You will need to work quickly, so have everything ready before you start.