If you love sandwiches as much as I do, then learning how to make this Copycat Subway Sweet Onion Sauce will elevate your sandwich game!
There’s nothing quite like that tangy-sweet punch from Subway’s sweet onion sauce. If you’re looking for a special sauce you could drizzle over your homemade subs, salads, or wraps, this copycat recipe is it. This sauce is smooth, zippy, sweet with a hint of spice, and best of all, incredibly easy to make at home.
A Distinctively Delicious Sauce
Some condiments are just a cut above the rest. Personally, it’s Subway’s sweet onion sauce for me. This sauce just pulls together a footlong veggie sub or grilled chicken with its perfect balance of sweetness and tang. Even when I’m just making subs at home, this sweet onion sauce recipe is my go-to to finish off my homemade sandwiches. This Subway Copycat Sweet Onion Sauce is so easy, you can whip it up in under 30 minutes.
Recreating that bold yet smooth flavor was no small task. The key is real caramelized onions blended to silky perfection, a mix of red wine vinegar and white vinegar for acidity, and just the right touch of spices and sweetener.
With this Subway Copycat Sweet Onion Sauce, you can keep a jar in your fridge and enjoy it anytime. This is the perfect finishing touch to top your wraps, sandwiches, and even cooked chicken breast. I tried it with my copycat Costco Turkey and Provolone Sandwich, and it turned out even better!
Ingredients You’ll Need for Subway Copycat Sweet Onion Sauce
Here’s what you’ll need to make this Subway Copycat Sweet Onion Sauce. Scroll down to the recipe card at the bottom of the page for the detailed ingredient measurements.
- Sweet Onion: has to be thinly sliced and caramelized, because this is the flavor foundation. A yellow or Vidalia onion works great.
- Neutral Oil: like grapeseed or canola, are perfect for sautéing without altering the flavor of the rest of the ingredients.
- Red Wine Vinegar & White Vinegar: is the combination that brings acidity and depth to this sauce. Don’t skip the red wine vinegar, this is what adds complexity.
- Granulated Sugar: brings this homemade sauce that unmistakable sweetness.
- Dijon Mustard: will add body and that subtle tang to this recipe.
- Sesame Oil: in small amounts is all you’ll need. A little goes a long way because its distinct flavor might mask the other ingredients. It introduces a nutty undertone that makes the flavor pop.
- Cornstarch: is our thickener of choice because of the perfect syrupy texture it renders.
- Spices: such as onion powder, garlic powder, celery seed, paprika, black pepper, and salt, will balance the flavor.
- Poppy Seeds: add the visual signature of Subway’s sauce. Plus, it gives a slight crunch at the end.
Pro Tip: Use a microplane or even a cheese grater to finely mince your onion before caramelizing it.
How to Make a Subway Sweet Onion Sauce Recipe at home
- Caramelize the onions: To start, take a non-stick skillet and heat your neutral oil. Cook the thinly sliced sweet onion, seasoning with salt, for 10–12 minutes until golden and soft.
- Blend: Once the onion slices are caramelized, transfer to a blender with a bit of water. Then, blend it until very smooth. Run the blended onion over a fine mesh sieve to extract the ”onion juice”.
- Build the base: Next, pour the onion juice into a small saucepan. Add sugar, the vinegars, Dijon mustard, sesame oil, and all the spices. Whisk everything thoroughly altogether.
- Thicken: Combine cornstarch with 1 tbsp of water in a small bowl. Stir into the saucepan.
- Simmer: Heat the sauce over medium heat until it reaches a gentle boil. Allow the sauce to simmer for 2–3 minutes, stirring constantly until thickened and glossy.
- Finish: Remove the sauce from heat, allowing it to cool completely. Finally, stir in poppy seeds, and store in a jar or squeeze bottle in the fridge.
Tips and Tricks for Homemade Subway Sweet Onion Sauce Recipe
- Low and Slow is Key: Don’t rush the caramelization process. Let the onions turn golden brown for that deep flavor.
- Strain Well:It’s important to remove any pulp so you can achieve that signature smooth texture. A fine mesh strainer does the job perfectly.
- Cool Before Storing: Let your Subway Copycat Sweet Onion Sauce cool completely before bottling it, to avoid condensation and keep the texture just right.
- Customize Spice: If you prefer a little more heat, you can add a pinch of cayenne or crushed red pepper.
Why You’ll Love This Subway Copycat Sweet Onion Sauce
This Subway Copycat Sweet Onion Sauce may require a few extra steps, but I promise, making this recipe at home is so worth it. It tastes just like Subway’s sweet onion sauce. On top of that, you’re sure that this doesn’t contain preservatives, or mystery ingredients. It keeps really well in the fridge, and it’s perfect not just for wraps and sandwiches, but also cooked meat, veggies, and salads! Lastly, this is naturally dairy-free and gluten-free.
Frequently Asked Questions (FAQ's)
If stored carefully in a clean, airtight jar or bottle, this homemade sweet onion sauce can last up to 4 weeks.
Yes, you can. However, it’s the red wine vinegar that adds a unique depth. Balsamic or apple cider vinegar can be used as substitutes in a pinch.
Yes, it is! There are no animal products added in this recipe.
I don’t recommend it. If frozen, it might alter the texture once thawed.
This tasty sauce is so versatile. It works well on grilled chicken wraps, veggie subs, as a salad dressing, or even as a marinade.
Yes, you can. But they give the sauce that classic Subway look and a nice finish.
A small, sweet onion like Vidalia is the best for this recipe. But, a yellow onion works too.
If you want a chunky-textured sauce, go for it. Personally, I always go for the extra step of straining the sauce for best results.
Homemade Subway Sweet Onion Sauce Recipe
How to Make Subway Copycat Sweet Onion Sauce
Ingredients
- 1 small sweet onion thinly sliced
- 1 tsp neutral oil like grapeseed or canola
- 1/4 tsp salt for caramelizing onions
- 1/4 cup water for blending onions
- 1/2 cup granulated sugar
- 3 tbsp white vinegar
- 1 tbsp red wine vinegar for depth
- 1 tsp Dijon mustard adds tang and body
- 1/4 tsp sesame oil a little goes a long way!
- 1 tbsp cornstarch or potato starch
- 1 tsp onion powder
- ¼ tsp garlic powder
- ½ tsp salt for seasoning the sauce
- ¼ tsp celery seed
- ¼ tsp paprika
- ⅛ tsp ground black pepper
- ½ tsp poppy seeds optional, adds a bit of texture and visual
Instructions
- In a small nonstick skillet over medium heat, add oil, sliced onion, and ¼ tsp salt. Cook for about 10–12 minutes, stirring often, until deeply golden and soft. Reduce heat as needed to prevent burning.1 small sweet onion, 1 tsp neutral oil, 1/4 tsp salt
- Transfer caramelized onions to a blender with ¼ cup water. Blend until very smooth. Strain through a fine mesh sieve to extract onion “juice,” discarding any remaining pulp.1/4 cup water
- Pour the onion juice into a saucepan. Add sugar, both vinegars, Dijon mustard, sesame oil, and all the spices. Whisk to combine.1/2 cup granulated sugar, 3 tbsp white vinegar, 1 tbsp red wine vinegar, 1 tsp Dijon mustard, 1/4 tsp sesame oil, 1 tsp onion powder, ¼ tsp garlic powder, ½ tsp salt, ¼ tsp celery seed, ¼ tsp paprika, ⅛ tsp ground black pepper
- In a small bowl, mix cornstarch with 1 tablespoon of water to make a slurry. Add it to the saucepan.1 tbsp cornstarch
- Heat sauce over medium heat. Bring to a gentle boil, then lower heat and simmer for 2–3 minutes, whisking constantly, until thickened and glossy.
- Remove from heat and let cool completely. Mix in the poppy seeds, then transfer to a jar or squeeze bottle and refrigerate. Sauce will thicken slightly more as it cools. Keeps for up to 4 weeks in the fridge.½ tsp poppy seeds
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