Subway Sweet Onion Sauce

Why You’ll Love This Sweet Onion Sauce Recipe

If you were a Subway sweet onion sauce person, this recipe is going to hit. It’s sweet, tangy, and packed with that onion flavor that makes a plain sandwich taste way better. I used to get it on basically every sub I ordered from Subway, so when I started working on a homemade version, I wanted it to actually taste like the real thing.

The biggest difference-maker was the onion. I tested it with larger pieces at first, and the texture was off right away. Finely grating it made the sauce taste much closer to Subway’s because you get the onion flavor throughout without ending up with a chunky sauce.

I also like that it comes together quickly and keeps well once it’s made. The texture turns glossy and pourable on the stove, and after it chills, the flavor gets even better. It’s great on subs, wraps, salads, grilled chicken, and meal prep lunches, so it’s easy to use up a batch without trying.

Ingredients

This sauce uses pantry spices, vinegar, sugar, and a little fresh onion for that classic sweet onion flavor.

Here’s everything you’ll need:

• 1 cup granulated sugar
• ½ cup plus 1 tablespoon water
• 6 tablespoons white vinegar
• 4 ½ teaspoons red wine vinegar
• 1 teaspoon finely grated onion
• 1 tablespoon Dijon mustard
• ¼ teaspoon sesame oil
• 1 tablespoon cornstarch
• 1 tablespoon dried minced onion
• 2 teaspoons dry mustard powder
• 1 teaspoon salt
• ¾ teaspoon poppy seeds
• ½ teaspoon celery seed
• ¼ teaspoon onion powder
• Heaping ¼ teaspoon paprika
• Heaping ¼ teaspoon ground black pepper

How To Make Subway Sweet Onion Sauce

Step 1: Combine The Ingredients

Add the sugar, water, white vinegar, red wine vinegar, finely grated onion, Dijon mustard, sesame oil, cornstarch, dried minced onion, mustard powder, salt, poppy seeds, celery seed, onion powder, paprika, and black pepper to a small saucepan.

Whisk everything together until well combined and the cornstarch is fully mixed in.

Step 2: Bring To A Gentle Boil

Place the saucepan over medium-high heat. Bring the sauce to a gentle boil, whisking frequently so the sugar dissolves and the cornstarch doesn’t settle on the bottom.

Step 3: Simmer Until Thickened

Reduce the heat to low and let the sauce simmer for about 5 minutes. Continue whisking while it simmers. The sauce should thicken slightly and become glossy. It will continue to thicken a little more as it cools.

Step 4: Cool Completely

Remove the saucepan from the heat and let the sauce cool completely. The flavor will mellow as it cools, and the texture will become more like a pourable sandwich sauce or dressing.

Step 5: Store

Transfer the cooled sweet onion sauce to an airtight container or jar. Store it in the refrigerator for up to 4 weeks, or freeze it for longer storage.

Expert Tips For The Best Sweet Onion Sauce

• Grate the onion as fine as possible. I tested this with chopped onion first, and the sauce never tasted right. Finely grated onion blends into the sauce much better and gives you the onion flavor without little crunchy pieces.
• Whisk everything together before heating it. That’s the easiest way to keep the cornstarch smooth. If I add it once the liquid is already hot, it’s much easier to end up with lumps.
• Cook it over medium heat, not high. This sauce doesn’t need aggressive heat. A gentle simmer thickens it just fine and keeps the sugar from catching on the bottom of the pan.
• Keep whisking while it heats. The sugar, cornstarch, and spices settle quickly, so regular whisking helps the sauce thicken evenly and keeps the bottom from scorching.
• Stop once it looks glossy and slightly thickened. It should be loose enough to drizzle, not as thick as a creamy dressing. I’ve found it thickens more as it cools, so it’s better to pull it a little early than overreduce it.
• Let it cool fully before adjusting the texture. The first time I made it, I almost added more cornstarch too soon. Once it cools, it thickens enough to get much closer to that Subway-style consistency.
• Use both vinegars if you want the closest flavor. White vinegar gives the sauce that bright tang, while red wine vinegar makes it taste more rounded. When I tested it with just one, it always tasted like something was missing.
• Don’t skip the celery seed and poppy seeds. They seem small, but they’re part of what makes the sauce taste more like the real thing instead of just a sweet onion glaze.
• Be careful with the sesame oil. I tested stronger amounts, and it started taking over the sauce fast. A very small amount adds depth, but too much pulls it away from that classic sweet onion flavor.
• Taste it cold, not just warm. The flavor changes once it chills. I always do my final taste after it’s been in the fridge, because that’s when I can tell if it needs a little more tang, sweetness, or onion.

What To Use Sweet Onion Sauce On

This sweet onion sauce is especially good on sandwiches, but it works in a lot of other places too.

• Subs and sandwiches: turkey subs, chicken sandwiches, ham sandwiches, veggie subs, steak sandwiches, wraps, burgers, and breakfast sandwiches
• Salads and bowls: chopped salads, grilled chicken salads, turkey salads, crispy salad, and veggie bowls
• More ways to serve it: grilled chicken, crispy chicken, chicken tenders, fries, onion rings, roasted potatoes, and grilled vegetables

I use it most on homemade subs, but it also works really well anywhere you want something sweet, tangy, and a little more interesting than plain dressing or mayo.

Subway Sweet Onion Sauce FAQs

What is Subway sweet onion sauce made of?

Subway sweet onion sauce is a sweet, tangy onion sauce made with sugar, vinegar, onion, mustard flavor, and seasonings. This homemade version uses sugar, vinegars, grated onion, Dijon mustard, poppy seeds, celery seed, and spices to get close to that same signature flavor.

What does Subway sweet onion sauce taste like?

It tastes sweet, tangy, oniony, and slightly savory. The vinegar and sugar give it that sweet-and-tangy balance, while the onion and seasonings make it taste more like a sandwich sauce than a basic dressing.

Is this like Subway sweet onion sauce?

Yes, this recipe is made to taste like a Subway copycat sweet onion sauce. It has that same sweet, tangy, onion-forward flavor and works really well on subs, wraps, salads, and sandwiches.

How do you thicken sweet onion sauce?

Cornstarch thickens the sauce as it cooks. The best way to keep it smooth is to whisk the cornstarch into the cold liquid first, then simmer the sauce until it looks glossy and lightly thickened.

Can I make sweet onion sauce ahead of time?

Yes, and it actually tastes better after it sits in the fridge. Making it ahead gives the flavors more time to blend, which makes the sauce taste smoother and more balanced.

How long does homemade sweet onion sauce last?

Homemade sweet onion sauce will keep in an airtight container in the refrigerator for up to 4 weeks. Give it a shake or stir before using.

Does sweet onion sauce need to be refrigerated?

Yes. Since this is a homemade sauce, it should be stored in the refrigerator in a clean airtight jar or container.

What can I put sweet onion sauce on?

It’s especially good on turkey subs, chicken sandwiches, wraps, salads, veggie bowls, grilled chicken, and homemade Subway-style sandwiches. It also works as a dip for chicken tenders, fries, and roasted vegetables.

Copycat Sauce Recipes To Try Next

• Whataburger creamy pepper sauce
• Popeyes blackened ranch
• Frisco sauce
• Dave's hot chicken sauce
• Burger King zesty sauce