Ingredients:

  • 1.5 lbs (680g) beef sirloin, trimmed and cut into 1/2-inch thick slices
  • 1/4 cup (60ml) balsamic vinegar
  • 2 tablespoons (30ml) olive oil
  • 1 tablespoon (15ml) soy sauce
  • 1 tablespoon (12g) brown sugar, packed
  • 1 teaspoon (5ml) Dijon mustard
  • 1 clove garlic, minced (about 1 teaspoon)
  • 1/2 teaspoon dried thyme
  • Salt and freshly ground black pepper to taste
  • 2 large yellow onions, thinly sliced
  • 2 tablespoons (30ml) olive oil
  • 1 tablespoon (15ml) butter, unsalted
  • 1 teaspoon (5ml) brown sugar
  • 1/4 teaspoon salt
  • 12 brioche slider buns
  • 6 ounces (170g) brie cheese, rind removed and sliced
  • 2 tablespoons (30g) butter, melted
  • Fresh thyme sprigs (optional)

Instructions:

  1. Combine balsamic vinegar, olive oil, soy sauce, brown sugar, Dijon mustard, garlic, thyme, salt, and pepper in a bowl. Add the beef slices and toss to coat. Marinate for at least 30 minutes, or up to 2 hours in the refrigerator.
  2. Heat olive oil and butter in a skillet over medium-low heat. Add onions, brown sugar, and salt. Cook, stirring occasionally, until onions are deeply golden brown and softened (about 20-25 minutes).
  3. Heat the skillet over medium-high heat. Remove beef from marinade (reserve the marinade!). Sear the beef slices for 2-3 minutes per side, or until cooked to desired doneness. Add the reserved marinade to the pan during the last minute of cooking to create a glaze.
  4. Preheat oven to 350°F (175°C). Slice the brioche buns in half. Brush the cut sides with melted butter. Place the bottom buns on a baking sheet.
  5. Top each bottom bun with caramelized onions, a slice of brie, and a piece of balsamic-glazed beef.
  6. Place the top buns on the sliders. Bake for 5-7 minutes, or until the brie is melted and the buns are lightly toasted.
  7. Garnish with fresh thyme sprigs (optional) and serve immediately.