Ingredients:
For steak:
• 2 pounds flank steak
• 1/3 cup oil
• 1½ tablespoon Worcestershire sauce (or soy sauce)
• 3 cloves garlic, finely minced (or ½ tsp garlic powder)
• 1 teaspoon kosher salt
• ½ tsp freshly ground black pepper
For sauce:
• 1 cup sour cream
• 1½ to 2 tablespoon prepared horseradish (adjust to taste)
• 1 teaspoon fresh lemon juice
• ¼ teaspoon kosher salt
• pinch of freshly ground black pepper
For onions:
• 2 tablespoon butter
• 4 cups yellow onions, thinly sliced (about 2 large onions)
• 1/2 teaspoon paprika
• ¼ teaspoon salt
For assembly:
• 12 slices French baguette slices, toasted
• paprika, for dusting
• chopped fresh chives or flat-leaf parsley (optional, for garnish)
Directions:
• In a shallow baking dish or large zip-top bag, whisk together the beer, oil, Worcestershire sauce, minced garlic, 1 tsp salt, and ½ tsp black pepper.
• Add the flank steak, turning to coat evenly.
• Cover and refrigerate overnight (or at least 6–8 hours).
Sauce:
• In a small bowl, whisk together the sour cream, prepared horseradish, lemon juice, ¼ tsp salt, and pepper until smooth.
• Taste and adjust heat with extra horseradish if desired. Cover and chill in the refrigerator until ready to serve.
Onions:
• Melt the butter in a wide skillet over medium heat.
• Stir in the paprika and ¼ tsp salt until fragrant, about 30 seconds.
• Add the sliced onions and toss to coat in the spiced butter.
• Cook over medium-low heat, stirring occasionally, until soft, sweet, and lightly golden-brown around the edges (about 15–20 minutes). Keep warm.
Steak:
• Position your oven rack 4 to 6 inches below the broiler element and preheat the broiler on High.
• Remove the steak from the marinade and discard the liquid.
• Thoroughly pat the steak dry with paper towels on both sides (removing excess moisture ensures a deep, charred sear rather than steaming).
• Place the steak on a foil-lined broiler pan or a wire rack set inside a rimmed baking sheet.
• Broil for 5–7 minutes per side, flipping once, until an instant-read thermometer inserted into the thickest part reads 130°F–135°F for medium-rare (or 140°F for medium).
• Transfer the steak to a cutting board, tent loosely with foil, and let it rest for 8 to 10 minutes so the juices redistribute.
Assembly:
• Using a sharp knife, slice the rested steak thinly across the grain at a 45-degree angle.
• Arrange 2 toasted baguette slices on each plate.
• Layer generous ribbons of warm sliced steak over the bread, followed by a mound of the warm, buttery onions.
• Dollop or drizzle the chilled horseradish cream over top.
• Finish with a light dusting of sweet paprika and fresh herbs, if using. Serve warm.
