Make a double batch of the horseradish spread to have on hand for burgers, steaks, and hot dogs.
Roast Beef and Caramelized Onion Sandwiches
- 2 tablespoons olive oil
- 2 cups (½-inch-thick) sliced red onion (about 1 large onion)
- 1 tablespoon balsamic vinegar
- 1 teaspoon kosher salt, divided
- 2 tablespoons unsalted butter, softened
- 8 slices sourdough sandwich bread
- ½ cup sour cream
- 2 tablespoons prepared horseradish
- 1½ teaspoons Dijon mustard
- 1½ cups fresh arugula
- 12 ounces thinly sliced deli roast beef, heated if desired
- In a 12-inch cast-iron skillet, heat olive oil over medium-high heat. Add onion; cook, stirring occasionally, until onion begins to soften and brown, 5 to 8 minutes. Stir in vinegar and ½ teaspoon salt. Reduce heat to low; cover and cook, stirring occasionally, until onion is browned and tender, about 10 minutes. Remove onion from skillet; wipe skillet clean.
- Spread butter onto one side of all bread slices. In same skillet, cook bread slices over medium-high heat until browned on both sides, 2 to 3 minutes per side.
- In a small bowl, stir together sour cream, horseradish, mustard, and remaining ½ teaspoon salt; spread mixture onto plain side of 4 bread slices. Top with arugula, onion, roast beef, and remaining 4 bread slices, buttered side up. Serve immediately.