Sweet Onion Sauce (Copycat)

If you’ve ever had a Subway sandwich, you know that their sweet onion sauce is the secret to adding rich, tangy-sweet flavor to every bite. But what if you could make a homemade version that’s even fresher, healthier, and free from preservatives? This easy sweet onion sauce recipe comes together in just 15 minutes using simple, pantry-friendly ingredients.

With its perfect balance of sweetness and acidity, this sauce is ideal for sandwiches, wraps, grilled meats, roasted veggies, and salads. Whether you’re meal prepping or looking for a new favorite homemade condiment, this Subway-inspired sweet onion sauce is a game-changer.

I used to buy bottled sweet onion sauce, but once I realized how easy it is to make at home, I never looked back! Fresh onions and vinegar give this sauce a natural tang, while poppy seeds and potato starch create the perfect smooth, slightly thickened texture.

Essential Ingredients for Sweet Onion Sauce

• Onion (1 medium, white or yellow): White onions give a mild, balanced sweetness, while yellow onions add depth.
• Sugar (¼ cup): Balances the acidity; use cane sugar, coconut sugar, or maple syrup.
• White Wine Vinegar (⅓ cup): Adds a mild tang; you can substitute with apple cider vinegar or rice vinegar.
• Poppy Seeds (1 teaspoon): Adds a light crunch and nutty flavor.
• Potato Starch (1 tablespoon, mixed with 2 tablespoons water): Thickens the sauce; cornstarch works as an alternative.

💡 Pro Tip: If you want extra depth of flavor, add ½ teaspoon garlic powder or a splash of soy sauce for umami!

Step-by-Step Instructions for Making Sweet Onion Sauce

Step 1: Prepare the Onion Juice

Chop the onion and blend with ½ cup of water until smooth.

Strain through a fine-mesh sieve, pressing with a spoon to extract as much liquid as possible.

Skip this step if you prefer a chunkier sauce.

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Step 2: Cook & Thicken the Sauce

In a small saucepan, heat the strained onion juice over medium-low heat.

Stir in sugar, white wine vinegar, and poppy seeds.

Prepare a slurry by mixing potato starch (or cornstarch) with 2 tbsp water.

Slowly pour the slurry into the saucepan while stirring continuously.

Bring to a gentle boil, then reduce heat and simmer for 2-3 minutes until syrupy.

Remove from heat and let cool.

Step 3: Cool & Store the Sauce

Let the sauce cool completely before transferring it to a glass jar or airtight container.

Store in the refrigerator for up to 1 month or freeze for longer storage.

Serving Suggestions: The Best Ways to Use Sweet Onion Sauce

• 🍔 Drizzle over sandwiches, burgers, or paninis: Adds a sweet and tangy kick.
• 🥗 Use as a salad dressing: Perfect for quinoa salads, spinach salads, or coleslaw.
• 🍗 Brush over grilled chicken or roasted meats: Works as a glaze or marinade.
• 🍕 Pair with pizza: Sweet onion sauce + savory meats = a match made in heaven.
• 🥦 Dip roasted or steamed veggies: A delicious alternative to ranch or honey mustard.

Storage & Freezing Instructions

• ✔ Refrigerator Storage: Store in an airtight container for up to 1 month. Shake or stir before using.
• ✔ Freezer Storage: Freeze in small portions using an ice cube tray. Once frozen, transfer to a freezer-safe container and store for up to 3 months.
• ✔ Thawing: Thaw in the fridge overnight before using.

Frequently Asked Questions

• Can I use red onions instead of white or yellow? Yes, but red onions have a stronger taste. Add extra sugar to balance the acidity.
• Why is my sauce too thin? The sauce thickens as it cools. If still too thin, return to the stove and simmer with an extra teaspoon of starch slurry.
• Do I have to strain the sauce? No! If you like a chunkier texture, skip the straining step.

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Final Thoughts: The Best Sweet Onion Sauce You'll Ever Make!

This homemade sweet onion sauce is a must-try for anyone who loves bold, tangy, and slightly sweet flavors. Whether you’re drizzling it over sandwiches, using it as a dip, or glazing your favorite proteins, it’s a versatile condiment that elevates every dish.

Plus, since it’s made from scratch, you get better flavor, no preservatives, and a completely budget-friendly option. Once you try this easy sweet onion sauce recipe, you’ll never go back to store-bought again!

🔥 Make it today and take your meals to the next level! 🍽️✨

Frequently Asked Questions

→ How long does this sauce last?

It stays fresh for up to 1 week in the refrigerator in an airtight container.

→ Can I use cornstarch instead of potato starch?

Yes! Cornstarch works the same way to thicken the sauce.

→ Is this sauce gluten-free?

Yes, all ingredients used are naturally gluten-free.

→ What can I use this sauce for?

It’s great on sandwiches, salads, wraps, and even grilled meats.

→ Can I make this sauce spicier?

Yes! Add a pinch of red pepper flakes or a dash of hot sauce for some heat.