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R-Rated Onions

This essential vegan recipe for slow-caramelised onions transforms humble store-cupboard staples into a decadent, savoury garnish. By slicing the onions with the grain and cooking them gently over a low heat, you coax out their natural sugars until they reach a deep mahogany hue. The result is a soft, fragrant, and incredibly versatile side dish that provides a sophisticated flavour profile for a variety of meals.

These versatile onions are a fantastic way to add a gourmet touch to homemade burgers, tarts, or even a simple cheese toastie. Prepared with just onions, oil, and salt, this batch-cook favourite is naturally plant-based and gluten-free. They keep well in the fridge for up to a week or can be frozen for three months, making them a practical addition to your weekly meal prep routine.

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Ingredients for R-Rated Onions

  • 4–5 large or 6–8 medium yellow or white onions

  • 1 tablespoon olive or vegetable oil

  • 1 teaspoon kosher salt

Peel your onions and cut them in half through their stem ends—longways, if you will. Slice them thinly with the grain, following the line from root to stem rather than cutting the onion across its belly. This is actually important because slicing it the other way makes the path to silky onions a longer one.

Once your onions are sliced, heat your skillet over medium-high heat and add the oil, then the onions and the salt. Let the onions sizzle for a couple minutes. Stir with a wooden spoon or a heatproof spatula and watch as they wilt for about 3 more minutes. At this point, reduce the heat to medium low. Put a lid on and step away for a few minutes. Give the onions a stir every now and then. You don’t have to stand over it like risotto, but don’t go for a walk around the block either. Caramelized bits will accumulate at the bottom and sides of the pan, and that’s good. Just scrape them up and stir them in. A little colour building as you go is okay, but don’t rush to brown them. The point is to cook the onions gently, coaxing them through stages of raw, wilted, sweaty, soft, light brown, and finally deeply caramelized

About 45 minutes in, remove the lid for the last time. They should be a light caramel colour. Now, with the lid off, you will need to watch more closely and stir more frequently. At some point you may find that despite your best efforts some of the caramelized bits, verging on burnt, cling to the pan and threaten over all onion ruin. Do not fret! Just add a 120ml or so of water and use its energy to help scrape up the stubborn but tasty film. Let the water cook out of course. When you’re smiling over a soft, creamy, fragrant pile of mahogany onions, you’re done.

Note: R-Rated Onions will keep in the fridge for a week and in the freezer for 3 months.

Disclaimer

While every effort has been made to ensure the information is accurate and up to date, individual needs may vary and dietary requirements can differ based on personal health conditions. Always check food labels and allergen information before preparing or consuming any recipe. If you have specific health concerns, allergies, intolerances, or are following a medically prescribed diet, seek advice from your GP, pharmacist, or a registered dietitian before making significant changes to your diet or lifestyle.

Article history

The information on this page is peer reviewed by qualified clinicians.

  • 28 Jan 2026 | Originally published

    Authored by:

    UK recipe editors

    Peer reviewed by

    UK recipe editors
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