How do I make a creamy mushroom sauce that does not go grey or split?

Browning the mushrooms properly before any liquid goes near them, why the sauce goes grey, and the cream and acid order that stops it splitting.

Difficulty: beginner
Time: 20 min
Read: 4 min

Short answer

Cook the mushrooms in a hot, uncrowded pan until the water has gone and they are properly browned — that takes eight to ten minutes and it is the whole sauce. Then shallot, garlic, a deglaze, stock, and double cream at the end. Salt the mushrooms only once they are brown.

Almost every disappointing mushroom sauce has the same cause: the mushrooms were stewed rather than browned. Mushrooms are around ninety per cent water, and until that water has evaporated the pan cannot get above 100°C and no browning can happen. Everything that makes a mushroom sauce taste of mushrooms happens after that point.

What you'll need

Mushrooms — chestnut, or a mixture
Wide frying pan
Butter and oil
Shallot or onion, garlic
Double cream
Stock (optional)
Dried porcini (optional)

Step by step

Slice the mushrooms thickly and get the pan properly hot.Thick slices survive the cooking; thin ones disintegrate. A wide heavy frying pan on a medium-high heat with a mixture of oil and butter — oil so it does not burn, butter for flavour.
Cook them in a single layer, in batches if necessary.This is the step everyone skips. A crowded pan traps steam and the mushrooms boil in their own liquid. Two batches take four minutes longer and produce a completely different sauce.
Leave them alone until the water has evaporated, then brown them.They will release liquid, sit in it, and look grey and unpromising for five minutes or so. Once the pan is dry they start to sizzle and colour. Give them another three or four minutes, turning occasionally, until there are proper brown edges.
Salt only after they are browned.Salt draws water out. Added at the start it prolongs the wet stage and prevents browning altogether. Added at the end it seasons them without cost.
Add shallot and garlic, then deglaze.A finely chopped shallot for two minutes, garlic for thirty seconds, then a splash of white wine, brandy, sherry or stock. Scrape the base until it is clean and let the liquid reduce to almost nothing.
Add stock, reduce, then cream.100ml of stock reduced by half, then 100–150ml of double cream. Simmer for two or three minutes until it coats a spoon. Double or whipping cream only — single cream splits when it boils.
Finish with acid, herbs and seasoning off the heat.A squeeze of lemon or a teaspoon of Dijon cuts the richness and makes it taste of mushrooms rather than of cream. Parsley, tarragon or thyme. Salt and plenty of black pepper. Add lemon off the heat so it cannot curdle the cream.

Tips

A small handful of dried porcini soaked in hot water, chopped and added with their strained soaking liquid, doubles the mushroom flavour of a sauce made from ordinary chestnut mushrooms.
Do not wash mushrooms under the tap if you can avoid it — brush or wipe them. They absorb water readily and it all has to be driven off again.
Chestnut mushrooms have more flavour than white ones for the same price. A few sliced shiitake add a great deal more.
For a pasta sauce, a ladle of the pasta cooking water at the end emulsifies with the cream and helps the sauce cling.
Crème fraîche instead of cream gives a sharper sauce and needs to go in off the heat, since it splits if boiled.

If it doesn't work

Grey, watery and tasting of nothing

Cause: The mushrooms stewed in their own liquid and never browned — Fix: Tip the sauce into a bowl, wipe the pan, and return the mushrooms alone to a hot dry pan to drive off the water and brown. Then rebuild.

The sauce split when the lemon went in

Cause: Acid added to boiling cream — Fix: Take the pan off the heat, whisk in a spoonful of cold cream, and add acid only off the heat in future.

Thin and milky

Cause: Single cream, or not enough reduction — Fix: Simmer to reduce further. If it is single cream it will split before it thickens; stabilise with a teaspoon of cornflour slurry instead.

Tastes flat despite properly browned mushrooms

Cause: No glutamate boost and no acid — Fix: A teaspoon of soy or a few rehydrated dried porcini plus their soaking liquid, and a squeeze of lemon at the end.

Questions people ask

Why do my mushrooms go grey and rubbery?

They are boiling rather than frying. Mushrooms release a lot of water in the first few minutes and if the pan is crowded, or not hot enough, or covered, that water cannot evaporate. The mushrooms then simmer in it, going grey, shrinking and turning rubbery. A wide, hot, uncrowded pan and the patience to wait through the wet stage is the entire fix.

Can I make it dairy-free?

Yes. Oat cream and cashew cream both work well and neither splits readily. Coconut cream works if the dish can carry the flavour. Alternatively, blend a quarter of the cooked mushrooms with a little stock and stir the purée back in — that gives body and an intensely mushroomy sauce with no cream at all.