Caramelized Onion Burger Recipe

This savory Caramelized Onion Burger is a bistro classic as well as being a masterclass in patience! Slow-cooking the onions makes them go jammy and sweet, which along with the sharp melted cheddar adds a rich, sophisticated flavor to this burger that is so satisfying on a toasted brioche bun.

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Caramelized Onion Burger Recipe Ingredients

• The Onions:
  • 2 medium sweet onions (like Vidalia), thinly sliced
  • 4 tbsp unsalted butter
  • Pinch of salt (and optionally sugar)
• The Burger Patties:
  • 1 lb lean ground beef (93% lean)
  • 1 tsp salt
  • 1/2 tbsp high-heat oil (canola or vegetable)
  • 1 tbsp butter (for the pan)
  • 4 slices sharp cheddar cheese
  • 4 brioche burger buns
  • Leafy lettuce (optional)
• The Garlic Herb Aioli:
  • 1/2 cup mayonnaise
  • 2 tbsp chopped fresh basil
  • 2 tbsp chopped fresh parsley
  • 1 tbsp chopped fresh rosemary
  • 2 garlic cloves, minced
  • Fresh cracked pepper (to taste)

How To Make Caramelized Onion Burger

1. Caramelize the onions: In a wide skillet, melt the 4 tbsp of butter over medium-low heat. Add the sliced onions and a pinch of salt. Cook slowly, stirring every few minutes, for 25–30 minutes. You want them soft, jammy, and deep golden brown. If they start to burn, lower the heat or add a splash of water. Set aside.
2. Make the aioli: While onions cook, whisk together the mayonnaise, basil, parsley, rosemary, minced garlic, and pepper in a small bowl. Refrigerate until ready to use (this helps the garlic flavor bloom!).
3. Prep the meat: Divide the ground beef into 4 equal portions. Gently roll them into loose balls. Do not pack them tight or form patties yet.
4. Heat the pan: Place a large cast-iron skillet over high heat. Let it get incredibly hot (smoking slightly), about 5 minutes.
5. Smash and sear: Brush the skillet with the oil and melt the tablespoon of butter. Place the beef balls into the hot pan. Immediately smash them flat with a heavy spatula (use a jar or mug to press down on the spatula if needed). Season generously with salt.
6. Flip and melt: Sear undisturbed for 2–3 minutes until a dark crust forms. Flip the patties. Top each with a slice of sharp cheddar. Cook for another 2 minutes until the cheese is melted and the burger is cooked through.
7. Assemble: Toast your brioche buns. Spread a generous layer of garlic herb aioli on the bottom bun. Add lettuce, then the cheesy patty. Pile a mountain of caramelized onions on top. Cap it and serve immediately.

Recipe Tips!

• Onion Patience: You cannot rush caramelized onions! High heat burns them. Low and slow breaks down the sugars. If you are desperate, a pinch of sugar helps them brown faster, but time creates the best flavor.
• The Smash: Smashing the burger into the hot pan creates the “Maillard reaction”—that dark, crispy, savory crust that makes diner burgers taste so good. Do it within the first 30 seconds of cooking, then stop touching it!
• Loose Meat: Don’t overwork the beef when making balls. Handling it too much melts the fat and makes the burger tough. Keep it loose and shaggy for a tender bite.
• Aioli Storage: The garlic herb aioli tastes even better the next day! Make a double batch and use it for dipping fries or spreading on sandwiches later in the week.

What To Serve With Caramelized Onion Burger?

This Caramelized Onion Burger Recipe is a gourmet meal that needs high-quality sides! A basket of Truffle Fries or Sweet Potato Wedges is the perfect match for the rich onions. For a lighter touch, a crisp Wedge Salad with blue cheese dressing cuts through the beef fat perfectly! To drink, a dark Amber Ale or a glass of Malbec pairs wonderfully with the sweet, caramelized notes of the onions.

How To Store Caramelized Onion Burger

• Refrigerate: Store the cooked patties, onions, and aioli in separate containers. The patties keep for 3 days; the onions and aioli for a week.
• Reheat: Reheat the patty in a skillet with a splash of water (covered) to steam the cheese back to life without drying out the meat. Warm the onions in the microwave.
• Freeze: Raw beef balls freeze well. Cooked patties can be frozen but lose some texture. Do not freeze the aioli or the lettuce!

Caramelized Onion Burger Nutrition Facts

• Calories: 650 kcal
• Fat: 42g
• Carbohydrates: 35g
• Protein: 32g

Nutrition information is estimated per burger.

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