Sometimes flavor lies in simplicity. A whole onion, slowly roasted, turns into something completely different: soft, sweet, almost creamy inside and lightly caramelized on the outside. In the oven they become deep and full of flavor, on the BBQ they pick up a subtle smokiness and even in the air fryer you can prepare them surprisingly well. Perfect as a side dish, a vegetarian highlight or as a flavor base for a healthy meal.

Ingredients (4 persons)

• 4 large yellow onions

• 3 tbsp olive oil

• 2 cloves garlic, finely chopped

• 1 tsp sea salt

• ½ tsp black pepper

• 1 tsp dried thyme or rosemary

• Optional: 1 tsp balsamic or honey for extra depth

Method – Oven

• Preheat the oven to 190°C (fan 180°C).
• Cut off the top cap of the onions and remove only the dry outer skin. Keep the onions whole so they retain their shape while cooking.
• Mix the olive oil with garlic, salt, pepper and herbs. Place the onions in a baking dish and brush the tops generously with the herb oil.
• Add a small splash of water or stock to the bottom of the dish to prevent drying out.
• Roast the onions 45–60 minutes until they are completely soft. A knife should glide through effortlessly.

Want extra caramelization? Add a drop of balsamic in the last 10 minutes.

Method – BBQ

• Heat the BBQ to indirect heat (180–200°C).
• Prepare the onions as above. Wrap them loosely in aluminum foil or place them in a cast-iron dish.
• Place them on the indirect part of the BBQ and close the lid. Let them cook 40–60 minutes until soft.
• For a lightly roasted top, you can place them over direct heat without foil for the last 5 minutes.

Method – Air fryer

• Preheat the air fryer to 180°C.
• Prepare the onions the same way: cut off the cap, remove the outer skin and rub with herb oil.
• Optionally cut a small cross in the top so heat can penetrate better.
• Place the onions in the basket (optionally on a piece of baking paper).
• Bake 20–30 minutes at 180°C. Check after 20 minutes to see if they are starting to soften. Large onions may need a little longer.

Want the onions extra soft and juicy? Place a small dish with a tablespoon of water in the basket or loosely cover the onions with aluminum foil for the first 10 minutes. This helps them retain moisture and cook more evenly.

Is this healthy?

Yes. Onions are low in calories and rich in fiber and antioxidants such as quercetin. Roasting releases natural sugars, making them taste sweet without adding sugar.

If you use a normal amount of olive oil, this remains a light and nutritious side dish that fits well within a healthy diet.

Serving tip

Serve the roasted onions with a fresh or slightly spicy low calorie sauce for extra contrast. Think of a creamy mustard sauce, a spicy chili variant or a light BBQ sauce. The natural sweetness of the onion pairs perfectly with a sauce with character, while the dish remains light and balanced.

Frequently asked questions about roasted whole onions

1. Why use yellow onions and not red onions?

Yellow onions are ideal for roasting because they contain more natural sugars and have a nice balance between sweet and savory. During cooking they caramelize evenly and develop a deep, full flavor.

Red onions are milder and slightly sweeter on their own, but they become soggier more quickly and lose their fresh, slightly spicy character during long cooking. They also don't brown as nicely in the oven. For truly golden-brown, intensely caramelized onions, it's best to choose yellow onions.

2. How do I know when the onions are done?

The onions are ready when you can cut through them with a knife without resistance. The outside should be golden brown and the inside soft and creamy. Larger onions may require a bit more cooking time, especially in the air fryer.

3. Can you prepare roasted whole onions in advance?

Yes, you can. You can cook them ahead and reheat later in the oven or air fryer at 170°C for 8–10 minutes. They keep well for 2 to 3 days in the refrigerator and are even tasty cold in a salad or on a sandwich.