Homemade Subway Sweet Onion Sauce Recipe

I finally recreated Subway’s Sweet Onion Sauce at home, a tangy sweet blend of vinegars, sugar, and Dijon mustard that is perfect for sandwiches, salads, or as a dip.

I never thought a sandwich sauce could make me pause, but this Homemade Subway Sweet Onion Sauce did. I kind of reverse engineered it, kept tasting and tweaking until a simple hit of sugar and a whisper of Dijon mustard woke up the whole thing.

It’s tangy, kinda sweet, and weirdly addictive so youll be tempted to put it on every sandwich and salad. I use it like one of my go to Homemade Condiments for quick flavor boosts, and sometimes I cant help but dunk fries in it.

Trust me you wont expect how good this is.

Ingredients

Ingredient Quantities

• 1 cup sugar
• 6 tablespoons white vinegar
• 1 1/2 tablespoons red wine vinegar
• 2 teaspoons dijon mustard

How to Make this

1. Put 1 cup sugar, 6 tablespoons white vinegar and 1 1/2 tablespoons red wine vinegar into a small saucepan and give it a quick stir so the sugar is evenly distributed.

2. Set the pan over medium heat and stir constantly until the sugar fully dissolves, about 3 to 4 minutes. Dont let it sit or the sugar can scorch.

3. Once dissolved, bring it to a very gentle simmer and lower the heat to maintain that, cooking 4 to 6 minutes while stirring occasionally; you want it to slightly thicken and look glossy.

4. Remove the pan from heat and immediately whisk in 2 teaspoons Dijon mustard until the sauce is smooth and fully combined.

5. Taste carefully — the flavors mellow as it cools so dont freak out if it seems sharp at first.

6. Let the sauce cool to room temperature; it will thicken more as it cools and the sugar syrup sets.

7. Pour the cooled sauce into a clean jar or squeeze bottle, press a lid on and give it a good shake to make sure everything’s blended.

8. Refrigerate at least 2 hours, preferably overnight, for best flavor. Shake or stir before using; keeps well in the fridge for a couple weeks.

Equipment Needed

1. Small saucepan, about 1 to 2 quarts, for dissolving the sugar and simmering the syrup
2. Measuring cup, for the 1 cup sugar and vinegars
3. Measuring spoons, for the tablespoons and teaspoons (6 tbsp, 1 1/2 tbsp, 2 tsp)
4. Whisk, to blend the Dijon in so the sauce is smooth
5. Heatproof spatula or wooden spoon, for constant stirring so the sugar dont scorch
6. Stove or cooktop, to heat and maintain a very gentle simmer
7. Clean jar or squeeze bottle with lid, for storing and shaking the cooled sauce
8. Oven mitts or potholders, to handle the hot pan safely

FAQ

Homemade Subway Sweet Onion Sauce Recipe Substitutions and Variations

Homemade Subway Sweet Onion Sauce Recipe
Here are some easy swaps if you’re missing an ingredient or want to tweak the taste.

• Sugar: honey or agave nectar, use about 3/4 cup honey or 2/3 cup agave for 1 cup sugar, sauce may be a bit thinner so stir well.
• White vinegar: apple cider vinegar or rice vinegar, use the same 6 tablespoons, apple cider adds fruitiness, rice is milder.
• Red wine vinegar: sherry vinegar or white wine vinegar, use 1 1/2 tablespoons, sherry gives a closer depth of flavor.
• Dijon mustard: whole-grain mustard or yellow mustard, swap 1:1, whole-grain adds texture, yellow is milder and sweeter.

Pro Tips

– If the sugar starts clumping or burning on the pan, try adding 1 tablespoon of warm water right at the start. It helps the sugar dissolve more evenly so you wont get hot spots, and you can still reduce it down to the same glossy thickness.

– When you add the Dijon, whisk it into a couple tablespoons of the hot syrup first to make a smooth paste, then whisk that back into the rest. If it still looks grainy or it separates, blitz briefly with an immersion blender — saves salvaging the whole batch.

– Taste only after it cools a bit, the bite will calm down, but if it still feels too sharp, a tiny pinch of salt will round the flavors better than dumping in more sugar. Dont overdo it, a little goes a long way.

– For storage, use a sterilized jar, press plastic wrap on the surface before sealing if you want less skin, and keep it chilled. If it gets too thick in the fridge, warm the jar in hot water for a minute and give it a good shake to loosen it up.