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balsamic caramelized onion steak

Balsamic Caramelized Onion Steak Strips

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Prep Time 15 minutes
Cook Time 35 minutes
Resting Time 5 minutes
Total Time 55 minutes
Course Main
Cuisine American
Servings 4 servings

Equipment

  • 1 large heavy skillet or cast-iron pan
  • 1 Medium saucepan
  • 1 Cutting board
  • 1 Chef's knife
  • 1 Tongs
  • 1 Wooden spoon
  • 1 Measuring cups set
  • 1 Measuring spoons set
  • 1 Small bowl

Ingredients
  

  • 1 1/2 pound flank steak cut into 1/2-inch strips, patted dry
  • 2 tablespoon olive oil divided
  • 2 large yellow onions thinly sliced
  • 2 tablespoon unsalted butter
  • 1/2 teaspoon kosher salt for onions
  • 1/4 teaspoon black pepper for onions
  • 1/3 cup balsamic vinegar
  • 1 tablespoon brown sugar packed
  • 2 teaspoon Dijon mustard
  • 2 clove garlic minced
  • 1/2 teaspoon kosher salt for steak
  • 1/2 teaspoon black pepper for steak
  • 1 teaspoon fresh thyme leaves chopped
  • 1/4 cup beef broth low sodium
  • 1 tablespoon fresh parsley chopped, for garnish

Instructions
 

  • Pat the steak strips very dry with paper towels and season with 1/2 teaspoon kosher salt and 1/2 teaspoon black pepper.
  • Heat 1 tablespoon olive oil in the large skillet over medium heat and add the sliced onions with 1/2 teaspoon salt and 1/4 teaspoon pepper.
  • Cook the onions, stirring occasionally, until softened and deep golden, 15–20 minutes, lowering heat if browning too quickly.
  • Stir in butter and continue cooking onions 2 minutes to fully caramelize.
  • Add garlic to the onions and cook 30 seconds until fragrant.
  • Stir in balsamic vinegar, brown sugar, Dijon, thyme, and beef broth, then simmer 2–3 minutes until slightly syrupy; transfer onions and sauce to a bowl.
  • Return the skillet to medium-high heat, add remaining 1 tablespoon olive oil, and heat until shimmering.
  • Add steak strips in a single layer without crowding and sear 1–2 minutes per side until browned but still medium-rare; cook in batches if needed.
  • Reduce heat to medium, return all steak to the pan, and pour the balsamic onion mixture over the steak.
  • Toss to coat and simmer 1 minute to warm through and glaze the steak.
  • Remove from heat and let rest 5 minutes.
  • Garnish with chopped parsley and serve immediately.

Notes

For the best sear, ensure the steak is very dry and the pan is properly preheated before adding the meat, and avoid overcrowding by cooking in batches to prevent steaming. Slice flank steak against the grain to keep the strips tender, and aim to pull them slightly under your desired doneness since they’ll cook a touch more when glazed. If the onions threaten to scorch during caramelization, add a tablespoon of water to deglaze and lower the heat. You can swap flank steak for sirloin or skirt; thicker cuts may need an extra minute per side. Adjust sweetness by reducing or increasing the brown sugar, and for a richer sauce, whisk in a teaspoon of cold butter off heat.
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