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Subway Sweet Onion Sauce Recipe

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4.5 from 9 reviews

This Subway Sweet Onion Sauce recipe recreates the deliciously tangy and sweet condiment often found on Subway sandwiches. Made with blended onions and garlic, sweetened with sugar, and thickened with cornstarch, this sauce is perfect to enhance your homemade sandwiches and meals.

Ingredients

Scale

Vegetables & Aromatics

  • 1 medium-size onion
  • 2 garlic cloves

Liquids

  • ¾ cup water
  • ¼ cup water (for slurry)
  • 1 teaspoon balsamic vinegar
  • 1 teaspoon white vinegar
  • ½ teaspoon fresh lemon juice

Dry Ingredients & Seasonings

  • ⅓ cup granulated sugar
  • ¼ teaspoon nigella seeds/kalonji
  • ¼ teaspoon black pepper, freshly ground or to taste
  • ¼ teaspoon salt or to taste
  • 2 teaspoons cornflour/cornstarch

Instructions

  1. Blend onion and garlic: Peel the onion and garlic cloves, roughly chop them, then blend until smooth. Squeeze the blended mixture through a muslin cloth to extract the juice and transfer it to a pan or pot.
  2. Heat and combine ingredients: Place the pan over heat. Add ¾ cup water, granulated sugar, salt, white vinegar, balsamic vinegar, black pepper, and nigella seeds to the onion-garlic juice. Bring the mixture to a boil and stir until the sugar dissolves completely.
  3. Prepare cornstarch slurry: In a separate bowl, whisk together ¼ cup water with the cornflour until smooth to make a slurry.
  4. Thicken the sauce: Gradually add the cornstarch slurry to the boiling mixture while stirring continuously over medium flame. Continue stirring until the sauce thickens and becomes glossy.
  5. Finish and cool: Remove the pan from heat, add the fresh lemon juice, and stir to combine. Allow the sauce to cool to room temperature.
  6. Store the sauce: Transfer the sauce into an airtight container and refrigerate. Use the sauce as needed to add a sweet onion flavor to your dishes.

Notes

  • Use fresh onions and garlic for the best flavor.
  • Squeezing the juice through muslin cloth ensures a smooth sauce without pulp.
  • Adjust the sugar and vinegar to taste if you prefer sweeter or tangier sauce.
  • If nigella seeds are unavailable, you can omit or substitute with a pinch of cumin seeds for a different flavor.
  • This sauce keeps well refrigerated for up to one week.
  • For a thicker consistency, increase cornflour slightly, but add gradually to avoid lumps.