Prep time: 15 minutes
Total time: 30 minutes
1 medium shallot, thinly sliced into circles
2 tablespoons white wine vinegar
1 teaspoon kosher salt, plus more to taste
1 (1 pound|450 gram) piece of flank steak
6 tablespoons olive oil
1 baguette, halved lengthwise
4 ounces|½ cup|200 grams creme fraiche
2 tablespoons grated parmesan cheese
2 tablespoons prepared horseradish
1 tablespoon whole grain mustard
2 ounces|65 grams baby arugula
freshly ground black pepper, to taste
1. Toss the shallot with 1 teaspoon salt and the vinegar in a large bowl. Let sit for at least 10 minutes.
2. Meanwhile, light a grill. Brush the steak with 2 tablespoons oil and season all over with salt. Cook, flipping once, until medium-rare, 10 to 12 minutes. Transfer to a cutting board to rest 10 minutes before thinly slicing.
3. Brush the cut-side of the baguette with 2 tablespoons oil and grill on the cut-side until golden, about 3 minutes. Transfer to a cutting board.
4. Mix the creme fraiche, parmesan cheese, horseradish, and mustard in a bowl. Smear on the grilled sides of the baguette and top with slices of the steak. Toss shallots with the remaining 2 tablespoons olive oil, the arugula, and pepper. Top the steak with the salad mixture and place the top part of the baguette over the top. Serve.