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Subway Sweet Onion Sauce Recipe
5 from 63 votes

Subway Sweet Onion Sauce Recipe

Subway Sweet Onion Sauce is a versatile, tangy sauce made with blended sweet onion and garlic, sweetened with sugar and balanced with balsamic and white vinegar. Nigella seeds add a subtle herbal note, while a cornstarch slurry thickens the sauce to a glossy finish. This sauce is cooled and refrigerated to be used as a condiment, ideal for sandwiches and salads.

Prep Time
5 mins
Cook Time
10 mins
Total Time
15 mins
Servings: 1 cup
Course: Side Dish, Condiments
Cuisine: International

Ingredients

  • 1 onion medium-size
  • 2 garlic cloves
  • ¾ cup water plus ¼ cup water
  • ⅓ cup granulated sugar
  • 1 teaspoon balsamic vinegar
  • 1 teaspoon white vinegar
  • ¼ teaspoon nigella seeds aka kalonji
  • ¼ teaspoon black pepper or to taste, freshly ground
  • ¼ teaspoon salt or to taste
  • 2 teaspoon cornflour or cornstarch
  • ½ teaspoon lemon juice fresh

Instructions

    Cup of Yum
  1. Peel the onion and garlic, roughly chop them, and blend until look smooth. Squeeze the juice using a muslin cloth and transfer to a pan or pot.
  2. Heat the pan. Add in water, sugar, salt, white vinegar, balsamic vinegar, black pepper, and nigella seeds. Bring the mixture to a boil until sugar dissolves.
  3. Whisk ¼ cup water and cornflour together in a bowl, and make a slurry.
  4. Add the cornflour slurry and stir continuously over medium flame until the sauce thickens and looks glossier.
  5. Remove from heat and add lemon juice. Stir to mix and allow the sauce to come to room temperature.
  6. Store in an airtight container in the refrigerator and use when needed.

Notes

  • Taste the sauce before final storage to adjust seasoning and prevent over-seasoning.
  • Use any sweet onion variety such as Walla Walla, Texas sweets, Maui, or Vidalia for authentic sweetness; white or yellow onions also work.
  • Fresh garlic is preferred for flavor; garlic powder can substitute if fresh is unavailable.
  • White distilled vinegar and balsamic vinegar are used to provide acidity and depth.
  • Brown sugar may replace granulated sugar for a different sweetness profile.
  • Cornflour can be substituted with arrowroot, tapioca, or potato starch for thickening.
  • Freshly ground black pepper enhances flavor better than pre-ground.
  • Nigella seeds add a distinct oregano-onion flavor but can be omitted if unavailable.
  • Use cold filtered water for best results in sauce preparation.