Name: White Onion Sauce recipe
Cook time: 10 min
Total time: 10 min
Yield: 1
Ingredients: 40g butter; 2 tbs plain flour; 1 1/2 cups milk; 1/2 onion sliced; 1 tsp parsley to taste

by Natasha Shaw Last updated on 05/15/2025

A white sauce is nice, but add a little onion to it and it smacks with flavour. It takes mere minutes to make, and you can pour it over slices of pork, corned beef or silverside, or drown some cauliflower or other vegies in it to make them even more delish.

How to make white onion sauce: key tips

Start by cooking out the flour. Melt your butter in the saucepan, then add the flour and stir until it starts to bubble. Cooking the flour removes its raw taste and combining it with the butter creates a roux, preventing any lumps when the liquid is added. The result is a smooth and creamy sauce.

Remove the pan from the heat as you gradually stir in the milk. This will enable the milk to combine well with the roux you’ve just made and it won’t start scorching on the base of the pan.

Add the onion and then simmer, stirring constantly, until the sauce is deliciously thick. Stir in your parsley and you’re good to go!

Key ingredients in this white onion sauce recipe

The flour, butter and milk create the white sauce base for this recipe. Opt for full-cream milk for a creamier sauce.

White onion is generally preferred for an onion sauce as it will maintain the ‘whiteness’ of the sauce. You can certainly use brown onion in its place, but the colour of your sauce may be a little deeper, and brown onion does have a slightly more pungent flavour.

The parsley adds a fresh element to this rich sauce, plus a smattering of colour.

If you love white onion sauce, you’ll also love this caramelised onion gravy, and this cheesy white parsley sauce.

This recipe was originally submitted by proudmama, a member of the Australia’s Best Recipe community. Introduction and additional recipe notes by Natasha Shaw.

- Natasha Shaw

Ingredients

40g butter
2 tbs plain flour
1 1/2 cups milk
1/2 onion sliced
1 tsp parsley to taste

Method

Step 1

Melt butter in saucepan, add flour and stir until it starts to bubble.
Step 2

Remove from heat and while stirring, slowly add milk.
Step 3

Return to heat, add onion and bring to boil.
Step 4

Reduce heat and simmer for 2 minutes
Step 5

Remove from heat and add parsley to taste.

Recipe Notes

from Australia’s Best Recipes team

How could I adjust this white onion sauce?

Provide a little heat by adding ½-1 tbs cayenne pepper or ¼-½ tsp ground chilli. You could also add a handful of cheese to make it cheesy, or swap the parsley for garlic chives. A good sprinkling of freshly ground black pepper can also make a difference.

Can I make this white onion sauce ahead?

You can make this sauce up to 3 days in advance. Store it in a bowl in the fridge, with plastic wrap over the surface of the sauce to prevent a skin from forming.