Fish Bone Gravy for Roast Fish

Fish stock breaks every rule the meat ones follow. Twenty minutes and no longer, never any colour on the bones, and absolutely no boiling. Done right it is delicate and clean, and reduced with wine and finished with cold butter it makes a gravy good enough for a whole roast turbot.

Ingredients

Makes about 300ml, a generous ladle each

• 800g (1lb 12oz) white fish bones and heads turbot, sole, plaice or brill, gills removed
• 30g (1oz) butter for sweating
• 2 shallots finely sliced
• 1 stick celery sliced
• 1 leek white part only, sliced and washed
• 200ml (7fl oz) dry white wine
• 1 litre (1.75 pints) cold water
• 3 sprigs parsley stalks only
• 4 white peppercorns
• 100ml (3.5fl oz) double cream optional, for a richer sauce
• 80g (3oz) cold butter diced, to finish
• 1 tsp lemon juice
• sea salt and white pepper

Kit

• Wide saucepan
• Fine sieve
• Muslin
• Whisk
• Small ladle

Method

1. Wash the bones under cold running water for a couple of minutes until no blood runs off, and cut the gills out of any heads. Blood and gills are the two things that make fish stock bitter and grey, and both take thirty seconds to deal with.

2. Chop the bones so they fit the pan flat. Melt the 30g of butter in a wide pan and sweat the shallots, celery and leek over low heat for 5 minutes without letting them colour at all. A fish stock must stay pale, so if you hear any real sizzling turn it down.

3. Add the bones and stir for 3 minutes until they turn opaque and start to smell sweet rather than raw.

4. Pour in the wine and let it bubble for 2 minutes to cook off the harsh alcohol, then add the cold water and the parsley stalks and peppercorns.

5. Bring to just below a simmer and hold it there for exactly 20 minutes, skimming the white scum off. Twenty minutes is the limit. Beyond that fish bones release bitter compounds and the delicacy is gone for good. This is the opposite of every meat stock in this section.

6. Strain through a sieve lined with muslin without pressing on the bones at all. Pressing pushes fine particles through and clouds it.

7. Pour the strained stock into a wide pan and reduce hard to about 250ml, roughly 15 minutes. It should smell sweet and concentrated. Add the cream now if you want a richer sauce and bubble for 2 minutes.

8. Take the pan off the direct heat so the sauce is hot but not boiling, then whisk in the cold butter a few cubes at a time until it is glossy and slightly thickened. Add the lemon juice, season with sea salt and white pepper and serve immediately. It will not hold for long, so time it to the fish.

Tips worth knowing

• Flat fish bones are best. Turbot, brill, sole and plaice give a clean sweet stock. Oily fish like mackerel and salmon make a strong, greasy stock that overwhelms everything.
• Ask the fishmonger to bag the frames when they fillet for you. They usually cost nothing and they freeze well.
• Twenty minutes, timed. Set a timer, because it is genuinely the difference between elegant and bitter.
• Mounting with butter is a temperature game. Too hot and the emulsion splits, too cool and it will not come together. Aim for around 70C, just below a simmer.

Keeping and reheating

Fumet keeps two days in the fridge and three months frozen. The finished butter sauce does not keep and will split on reheating, so make it to order.

Questions people ask