Grilled Steak and Arugula Salad with White Beans and Shiitake

Peppery arugula, earthy mushrooms, caramelized onions, and white beans make a luxurious bed for leftover flank steak.

For the beans and mushrooms

• 2 Tbs. extra-virgin olive oil
• 4 cups thinly sliced red onions
• Kosher salt and freshly ground black pepper
• 1 lb. shiitake mushrooms, stemmed and sliced 1/2 inch thick (6 cups)
• One 15.5-oz. can cannellini or white beans, rinsed
• 1-1/2 Tbs. sherry vinegar
• 1 Tbs. finely chopped fresh thyme
• 1/4 tsp. crushed red pepper flakes

For the vinaigrette

• 1/4 cup sherry vinegar
• 2 Tbs. finely chopped shallots
• 1 Tbs. Dijon mustard
• 1/2 cup extra-virgin olive oil
• Kosher salt and freshly ground black pepper
• 1/2 lb. baby arugula (10 cups)
• 1 lb. leftover grilled flank steak, thinly sliced, preferably at room temperature

Prepare the beans and mushrooms

Heat the olive oil in a 12-inch skillet over medium-high heat until shimmering. Add the onions, season generously with salt and pepper, and reduce the heat to medium. Cook, stirring occasionally, until tender and caramel colored, 10 to 12 minutes. Add the shiitake and continue cooking, stirring occasionally, until wilted and soft, about 5 minutes. Off the heat, stir in the beans, vinegar, thyme, and pepper flakes. Season to taste with salt and pepper and let cool to room temperature.

Make the vinaigrette

In a small bowl, combine the vinegar, shallots, and mustard. Whisk in the olive oil in a steady stream. Season the vinaigrette to taste with salt and pepper.

Assemble the salad

In a large bowl, gently toss the arugula with enough of the vinaigrette to lightly coat. Season to taste with salt and pepper. Arrange the arugula in a large serving bowl or platter and top with the bean and mushroom mixture and the sliced steak. Drizzle with some of the remaining vinaigrette (you may not need it all) and serve.