Anna Louise Onion sauce is one of those traditional British condiments that has been quietly wonderful for centuries and that deserves much more attention than it gets.
It is essentially a béchamel enriched with properly softened, slightly sweet onions — creamy, gently flavoured, and completely delicious poured generously over roast lamb. It is also very good with sausages, with roast pork, and with boiled gammon.
The key is cooking the onions very gently until they are completely soft and sweet before they go into the sauce. Onions that are only briefly cooked give a slightly sharp, slightly raw note that persists in the finished sauce.
Onions cooked slowly for twenty minutes until yielding and slightly golden dissolve beautifully into the béchamel and give a sauce with genuine depth and sweetness.
Ingredients for Mary Berry Onion Sauce (Serves 6)
For the Onion Sauce
- 3 large onions, peeled, halved, and very finely sliced
- 40g unsalted butter — for cooking the onions
- 40g plain flour
- 500ml whole milk, warm
- 100ml double cream
- ½ tsp freshly grated nutmeg
- 1 bay leaf
- Salt and freshly ground white pepper
How to Make Mary Berry Onion Sauce
Step 1 — Cook the Onions
Melt the butter in a medium saucepan over a medium-low heat. Add the sliced onions and bay leaf. Cook very gently, stirring occasionally, for 18 to 22 minutes until the onions are completely soft, slightly translucent, and very lightly golden at the edges. They should be sweet and completely yielding — not browned or caramelised.
Do not rush this step. Underdone onions give a slightly harsh, slightly raw sauce.
Step 2 — Add the Flour
Sprinkle the flour over the soft onions. Stir continuously for two minutes over a medium heat until the flour is cooked into the onions and the mixture looks smooth and slightly golden.
Step 3 — Add the Milk
Add the warm milk gradually — a splash at a time at first, stirring constantly to prevent lumps. Once the sauce is smooth, add the remaining milk in a steady stream, whisking constantly.
Bring to a gentle simmer over a medium heat, stirring all the time, until the sauce is thick, smooth, and coats the back of a spoon generously. Cook for a further three to four minutes to make sure the flour is completely cooked out.
Step 4 — Finish
Remove the bay leaf. Add the double cream and freshly grated nutmeg. Season generously with salt and white pepper. Taste — the sauce should be creamy, subtly onion-flavoured, and well-seasoned. Adjust as needed.
Serve warm, poured generously over roast lamb or the chosen accompaniment.
My Top Tips For Perfect Mary Berry Onion Sauce
Cook the onions very gently for the full 18 to 22 minutes. I cannot say this strongly enough — the sweetness and softness of the onions is everything in this sauce. Quickly cooked onions give a sharp, slightly disappointing sauce. Slowly cooked, completely tender onions give a sauce that is specifically and wonderfully onion-flavoured.
Use warm milk. Adding cold milk to the hot roux causes lumps. Warm milk — thirty seconds in the microwave — incorporates smoothly and gives a lump-free sauce with much less effort.
Stir constantly when adding the milk. The moment stirring stops, lumps form. Keep stirring throughout the milk-adding stage and continue stirring as the sauce comes to the boil and thickens.
Add the cream at the end — off the heat. The double cream added off the heat at the very end gives a richness and silkiness to the finished sauce without any risk of it reducing too much or splitting.
Season assertively. Onion sauce needs confident seasoning to bring out the flavour of the onions. Taste before serving and add salt, white pepper, and nutmeg to the point where the sauce tastes properly flavoured.
Serving Suggestions
Poured generously over roast lamb — the most traditional and specifically correct pairing. Over boiled or roast sausages. Over roast pork. As a sauce for boiled gammon or bacon. Alongside baked jacket potatoes.
How to Store Mary Berry Onion Sauce
In the fridge: Store covered with cling film pressed directly onto the surface for up to 2 days. Reheat very gently in a saucepan with a splash of warm milk, stirring constantly. Freezing is not recommended — the sauce can split on defrosting.
Mary Berry Onion Sauce Recipe
Ingredients
Method
- Melt butter in a medium saucepan over medium-low heat. Add sliced onions and bay leaf. Cook very gently 18–22 minutes until completely soft, slightly translucent, and very lightly golden at the edges.
- Sprinkle flour over onions — stir continuously 2 minutes until smooth.
- Add warm milk gradually — a splash at a time — stirring or whisking constantly. Once smooth, add remaining milk in a steady stream. Bring to a gentle simmer, stirring continuously, until thick and glossy — 3–4 minutes more.
- Remove bay leaf. Add cream and nutmeg. Season generously with salt and white pepper. Taste and adjust. Serve warm.
Notes
Frequently Asked Questions
Can I make this in advance?
Yes — make the sauce up to two days ahead and refrigerate. Reheat gently with a splash of warm milk and stir until smooth and hot throughout.
Can I add mustard?
Yes — one teaspoon of Dijon mustard stirred in at the end gives a slight sharpness that suits sausages and gammon very well. Reduce the nutmeg slightly.
Can I make this without cream?
Yes — use all milk (600ml total) and add a small extra knob of butter at the end. The sauce will be slightly less rich but still very good.
Can I use onion powder instead of fresh onions?
Fresh onions cooked slowly give a completely different, far superior flavour to onion powder. I would not recommend the substitution — fresh onions are the point of this sauce.
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