By Simran Makkar
November 7, 2026
Anyone who has eaten a good sub knows the sauce does half the work, and sweet onion is usually the one people ask about. It’s not a mystery, though. It’s onions left alone on a low flame until they go dark and sticky, then loosened with a little vinegar and honey. Spoon it on a burger, a grilled chicken sandwich or even a leftover roti, and it makes the whole thing taste like you tried a lot harder than you did.
– 3 large onions, thinly sliced – 2 tablespoons butter or oil – 1 tablespoon honey or brown sugar – 2 tablespoons apple cider vinegar or white vinegar – 2 tablespoons soy sauce – 1 tablespoon tomato ketchup – 1 teaspoon garlic, finely chopped – ½ teaspoon black pepper – ¼ teaspoon red chilli flakes (optional) – Salt to taste – ¼ cup water
Heat the butter in a wide pan on low-medium heat. Add the onions with a pinch of salt and cook for 20-25 minutes, stirring now and then, until they turn deep golden and soft. Add the garlic in the last minute.
Stir in the honey, vinegar, soy sauce, ketchup, pepper, chilli flakes and water. Let it simmer for 5-6 minutes, until the sauce turns thick and sticky.
Taste and adjust the salt or sweetness. Let it cool, then blend it for a smooth sauce, or leave it chunky if you like the texture.
Store in a clean jar in the fridge for up to a week, and serve with burgers, sandwiches or grilled chicken.