Mary Berry Onion Sauce Recipe

Mary Berry’s onion sauce is a creamy, deeply flavoured classic white sauce with softened onions — the essential accompaniment to roast lamb and sausages.

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Prep Time 10

Cook Time 30

Total Time 40

Servings: 6 Portions

Course: Soup

Cuisine: British

Calories: 185

Ingredients Method Notes

Ingredients

Onion Sauce:
3 large onions halved and very finely sliced
40 g unsalted butter
40 g plain flour
500 ml whole milk warm
100 ml double cream
½ tsp freshly grated nutmeg
1 bay leaf
Salt and white pepper

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

Cook onions very gently for the full 18–22 minutes — the sweetness of the onions is the flavour.

Use warm milk — cold milk added to a hot roux causes lumps.

Stir constantly when adding the milk — the moment stirring stops, lumps form.

Add cream off the heat at the end — gives richness without splitting.

Season assertively — onion sauce needs confident seasoning to taste properly flavoured.