This little sauce might not shout for attention — but it definitely pulls its weight.
Delia Smith’s Onion Sauce is one of those simple, quietly brilliant recipes that turns a plain bit of meat or veg into something you actually want seconds of.
It’s creamy, mellow, and has that lovely sweetness onions get when you cook them down just right. Honestly, it takes barely 15 minutes, but it tastes like you’ve been faffing about for ages. And isn’t that what we all secretly want?
Why You’ll Love This Onion Sauce Recipe
- Takes less time than boiling the kettle (well, almost)
- Just five ingredients — no wild shopping trip required
- Goes with practically anything: chicken, pork, mash, veg, even fish
- Handy way to make leftovers feel like a proper meal
- Freezes well, in case you get the urge to batch up
Ingredients
- 40g butter — for richness and base flavour
- 2 tbsp plain flour — to thicken it up
- 1½ cups milk — use whole milk if you’ve got it
- ½ onion, thinly sliced — sweetens the sauce nicely
- 1 tsp chopped parsley (optional) — adds a touch of colour at the end
How to Make Delia Smith Onion Sauce
1. Melt the butter:
Small pan, medium heat. Once it’s melted, stir in the flour. Let it cook for a minute — don’t rush it. You want that flour taste gone.
2. Add the milk:
Take the pan off the heat and slowly pour in the milk while whisking. Back on the hob now.
3. Add the onion:
Drop in the sliced onion and bring the whole thing to a gentle boil.
4. Simmer:
Turn the heat down and let it bubble away for 2 minutes. That’s all it needs to soften up and infuse.
5. Finish:
Turn off the heat. Stir in parsley if you’re feeling fancy. That’s it.
Common Mistakes and How to Dodge Them
Why is my sauce lumpy?
You probably added milk too fast or didn’t whisk. Off the heat, slow pour, constant stir — works every time.
Tastes too floury?
You didn’t cook the flour long enough before the milk went in. Let it bubble for a good minute first.
Burning on the bottom?
Heat too high or not enough stirring. Gentle simmer, low and slow.
Too thin?
Let it simmer a bit longer or add a pinch more flour (mixed with a splash of water first).
Storage and Reheating
Fridge:
Pop it in a lidded jar or container — keeps for 3 days.
Freezer:
Yes, and it holds up well. Cool it fully, then freeze for up to 3 months. Defrost gently.
Reheating:
- Stovetop: Medium-low, stir often
- Microwave: 30-second bursts, stir between
- Oven: Not really ideal, but can work if it’s part of another dish
- Air fryer: Not really the sauce’s scene, to be honest
Frequently Asked Questions
How do I know when it’s ready to simmer?
As soon as it comes back to the boil after adding onions, turn it down and time 2 minutes. Simple as that.
How do I stop it from burning?
Stir constantly at the start. Butter and flour catch quickly if you leave them to it.
Can I add a bit of heat?
Yep — try a pinch of cayenne or mustard powder. Start small.
Can I make it sweeter?
A tiny pinch of sugar does the trick — especially if your onions are on the sharp side.
Nutrition Facts (Per Serving – Based on 4 Servings)
- Calories: 71 kcal
- Fat: 0.1g
- Saturated Fat: 0g
- Cholesterol: 0.4mg
- Sodium: 91mg
- Carbohydrates: 18g
- Sugars: 18g
- Fiber: 0.1g
- Protein: 0.3g
- Calcium: 14mg
- Iron: 0.1mg
- Potassium: 19mg
More Delia Smith Recipe:
Delia Smith Onion Sauce
Description
Delia Smith’s Onion Sauce is a creamy, savoury white sauce infused with sweet onion flavour — perfect for pairing with meats, veg, or anything needing a flavour boost. Quick, comforting, and incredibly easy.
Ingredients
Instructions
- Melt butter in a saucepan over medium heat. Stir in flour and cook for 1 minute.
- Remove from heat, whisk in milk slowly to avoid lumps.
- Return to heat. Add onion and bring to a boil.
- Reduce to a simmer and cook for 2 minutes.
- Turn off heat. Stir in parsley if using. Serve warm.
Notes
- Use whole milk for a richer flavour
- For a smoother finish, strain the onions out before serving
- Don’t skip the simmer — it helps the sauce thicken and mellow
- Stores well, so double the batch if you’re planning ahead