🧅 Caramelized Onion Sauce
This sauce captures the deep, sweet-savory flavor of properly caramelized onions in a creamy, spreadable form. The onions take time to cook down, but once they do, they melt into a base of sour cream and mayo for a sauce that tastes like French onion soup on a burger.
🧾 Caramelized Onion Sauce — Recipe Card
From I Love Hamburger — ilovehamburger.com
Ingredients
- 2¾ large yellow onions, thinly sliced (about 450 g)
- 1¾ tbsp butter (14 g)
- 1¾ tbsp olive oil (15 ml)
- 0.5 tsp balsamic vinegar (2.5 ml)
- 0.25 cup sour cream (60 g)
- 2¾ tbsp mayonnaise (28 g)
- Salt and black pepper to taste
Instructions
- Melt the butter with the olive oil in a skillet over medium-low heat. Add the sliced onions and a pinch of salt.
- Cook slowly, stirring every few minutes, 25–30 minutes until the onions are deep golden brown and jammy. Lower the heat if they start to scorch.
- Stir in the balsamic vinegar and cook 1 minute more, then remove from the heat and let cool completely.
- Chop the cooled onions finely and fold them into the sour cream and mayonnaise. Season with salt and pepper.
- Chill 15 minutes before serving.
🫙 Storage
Airtight in the fridge for up to 5 days. The cooked onions keep well, but the sour-cream base limits it to about that window. Do not freeze once combined.
🔁 Substitutions
- Cook the onions a day ahead to split up the work; the sauce then comes together in minutes.
- Add a spoon of grated Gruyère while the onions are warm for a French-onion-soup twist.
🍔 What to put it on
Pair it with melted Gruyère or Swiss and sautéed mushrooms. It especially shines on these burgers:
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Frequently asked questions
How long does it really take to caramelize onions?
Real caramelization takes 25–35 minutes over medium-low heat — there is no true five-minute shortcut. Cooking them too hot browns the outside without developing the deep, even sweetness you want, so be patient and stir often.
Can I make the onions ahead?
Absolutely. Caramelize a big batch, refrigerate for up to 5 days, and stir a portion into the creamy base whenever you want the sauce. The cooked onions also freeze well on their own.