Hanger Steak with Charred Scallion Sauce

• ½ cup crushed or coarsely chopped walnuts
• 1 small garlic clove
• 9 Tbsp. extra-virgin olive oil, divided
• 1 1½-lb. hanger steak, cut into 4 pieces, center membrane removed

Kosher salt, freshly ground pepper

• ¾ tsp. Aleppo-style pepper, plus more for serving
• 12 scallions
• 5 tsp. sherry vinegar or red wine vinegar
• 1 Tbsp. chopped cornichons
• 1 Tbsp. chopped drained capers
• 1 Tbsp. whole grain mustard
• ¾ tsp. chopped thyme

Pinch of sugar

Flaky sea salt

1. Preheat oven to 350°. Toast walnuts on a rimmed baking sheet, tossing once, until golden brown, 8–10 minutes. Transfer to a medium bowl. Finely grate garlic over warm walnuts and toss with 6 Tbsp. oil.
2. Heat a large cast-iron skillet over medium-high. Season steaks with kosher salt and black pepper; sprinkle all over with Aleppo-style pepper. Rub with 2 Tbsp. oil and cook, turning occasionally, until deeply browned and an instant-read thermometer inserted into the thickest part registers 130° for medium-rare, 10–12 minutes. Transfer steaks to a cutting board.
3. Wipe out skillet and reduce heat to medium. Place scallions and 1 Tbsp. oil in skillet, season with kosher salt, and cook, turning occasionally, until softened and deeply charred, about 4 minutes. Transfer to cutting board; trim and cut into 1" pieces. Add to bowl with walnut mixture along with vinegar, cornichons, capers, mustard, thyme, and sugar and toss to combine; season with kosher salt and black pepper.
4. Slice steak against the grain and sprinkle with sea salt. Serve with scallion sauce and more Aleppo-style pepper.