Sweet onion sauce in a glass jar with spoon of sauce in front and sub sandwiches in background.

Sweet Onion Sauce Recipe

  • Author: Christine Pittman
  • Prep Time: 10 minutes
  • Rest Time: 30 minutes
  • Cook Time: 15 minutes
  • Total Time: 55 minutes
  • Category: Sauce
  • Method: Stovetop
  • Cuisine: American


Make a Subway Sweet Onion Sauce copycat with this delicious recipe. Perfect on sandwiches and salads!

Listen to learn how to make this recipe, along with some great tips from Christine:

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  • 1/2 tsp. neutral oil, like grapeseed
  • 1 large sweet onion, peeled, sliced thin
  • 1 tsp. salt, divided
  • 1/4 cup water
  • 1/2 cup granulated sugar
  • 3 Tbsp. white vinegar
  • 1 and 1/4 tsp. cornstarch
  • 1 tsp. onion powder
  • 1/2 tsp. garlic powder


  1. Preheat a small nonstick skillet over medium heat. Add oil, onions, and ¼ teaspoon of the salt. Cook, stirring occasionally, until onions are soft and well browned, about 12 minutes. Adjust heat as needed to prevent burning.
  2. Transfer onions to a blender. Add water and remaining ¾ teaspoon of the salt. Blend until smooth.
  3. Transfer onion mixture to a fine mesh sieve. Strain liquid from onion mixture into same skillet until onion mixture is nearly dry.* Add sugar, vinegar, cornstarch, onion powder, and garlic powder to skillet. Whisk until no lumps remain.
  4. Heat skillet over medium-high heat. Bring to boiling, reduce to a simmer. Cook, whisking constantly 2 to 3 minutes. 
  5. Remove skillet from heat, let cool at least 30 minutes. Transfer mixture to a container. Refrigerate until ready to use.

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*Save the onion pulp for other recipes, like onion jam, soups, or mashed potatoes.