Cheese and Onion Toastie
A toastie maker only cooks for about 4 minutes, which is not long enough to soften raw onion. That's why so many cheese and onion toasties end up with crunchy, sharp onion in them. The fix is to chop the onion very finely, salt it for 10 minutes, squeeze it dry and mix it into the grated cheese with a teaspoon of mayo. The onion softens and the filling holds together like the inside of a cheese and onion pasty.
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Recipe: Cheese and onion toastie
Ingredients
- 2 slices medium-cut white bread
- 55g mature cheddar, coarsely grated
- 1/4 small white onion (about 25g), very finely chopped, or 1 spring onion, thinly sliced
- 1 small pinch salt
- 1 tsp mayonnaise
- 1 small pinch white or black pepper
- 10g salted butter, softened
Method
- Chop the onion as finely as you can, into pieces about 2–3mm. Small pieces soften much faster than large ones.
- Put the onion in a bowl with a small pinch of salt, mix and leave for 10 minutes. The salt draws out water and takes the harsh edge off the onion.
- Meanwhile, close the toastie maker and preheat it until the ready light comes on.
- Tip the onion onto kitchen paper and squeeze it firmly to get rid of the liquid.
- Mix the onion, grated cheese, mayonnaise and pepper with a fork until the mixture clumps together.
- Butter one side of each slice. Put one slice buttered side down on the bottom plate.
- Press the cheese and onion mixture into an even layer in the middle, leaving a 1cm border.
- Put the second slice on top, buttered side up, and close the lid.
- Cook for 4 minutes in a standard machine or 5 in a deep fill. Rest for 1 minute before cutting.
Why salt the onion?
Raw onion is mostly water, and its sharp taste comes from sulphur compounds released when it's cut. Salting draws out some of that water, which softens the pieces and takes away some of the sharpness. Squeezing gets rid of the liquid, so it doesn't steam the bread from the inside.
The mayo binds the mixture. It coats the cheese and onion so they melt into one layer instead of the onion collecting in loose bits that fall out when you cut it. It also makes the melt slightly creamier, which suits strong cheddar.
Which onion to use
| Onion | Prep | Result |
|---|---|---|
| White onion | Finely chop, salt 10 min, squeeze | Classic pasty-shop flavour |
| Red onion | Finely chop, salt 10 min, squeeze | Slightly sweeter, pink flecks |
| Spring onion | Slice thinly; no salting needed | Mild and fresh; the quickest option |
| Shallot | Finely chop, salt 5 min | Sweetest raw option |
| Caramelised onion | Fry 20 min, cool fully | Rich and sweet; see variations |
Spring onion is the shortcut if you don't have time to salt it. Use the white and pale green parts and add a few slices of the dark green tops for colour.
The cheese
Strong mature cheddar stands up to onion. A crumbly Lancashire is a traditional pairing in the North West, but on its own it melts unevenly, so mix it half and half with cheddar. There are more options in our best cheese for toasties guide.
Other appliances
In a frying pan, use medium-low heat with a lid on for 3–4 minutes per side. The longer cook softens the onion a little more, so you can skip salting spring onion entirely. See the frying pan toastie method. In an air fryer, cook it at 180°C for 8 minutes, turning it halfway. A panini press needs 5 minutes, and the filling should stay 1.5cm from the edge because nothing seals.
Variations
- Caramelised onion and cheddar: fry 1 sliced onion in butter on low heat for 20 minutes and cool it completely. Use 2 tbsp of it, and keep it away from the edges, because the sugars catch on the plates.
- Cheese, onion and potato: add 40g cold leftover mash mixed into the cheese for a pasty-style toastie. It's best in a deep fill machine.
- Cheese and chive: use 1 tbsp of snipped chives instead of onion. There's nothing to salt.
- Red onion and red leicester: this one's sweeter and orange-coloured.
- Cheese, onion and chutney: add a thin smear of chutney, which links well with our classic cheese toastie variations.
Mistakes to avoid
- Thick onion rings: they stay raw and pull the cheese out in one piece when you bite.
- Skipping the squeeze: the onion water steams the bread so it goes soggy instead of crisp.
- Too much onion: keep it to about a third of the volume of the cheese, or the filling won't hold together.
- Filling up to the edge: onion in the seal stops the bread crimping. See how to stop toasties leaking.
For more ideas, see our toastie filling ideas. If your machine leaks with any filling, our cheese toastie maker picks favour plates with deep sealing edges.
FAQs
Should I cook the onion first?
You don't have to. Finely chopped, salted onion softens enough in 4 minutes. Pre-cook it only if you want caramelised sweetness, and let it cool before it goes into the toastie.
Is it like a Greggs cheese and onion bake?
It's the same flavour idea: mature cheese, soft onion and a creamy binder. The toastie is crisp bread rather than pastry, and the mayo gives you a similar creamy texture.
Can I prepare the filling in advance?
Yes. The cheese and onion mixture keeps covered in the fridge for up to 2 days. It actually mellows overnight as the salt keeps working on the onion.