You'll see fibers running through the cooked steak; make sure to cut across them for tender slices.
- 3 Thai or serrano chiles, with seeds, thinly sliced into rounds
- ¼ cup tamarind concentrate
- 3 tablespoons light brown sugar
- 1 tablespoon plus 4 tsp. vegetable oil
- 1½ pound skirt steak, cut into 4 pieces
- Tamarind concentrate, often labeled “concentrate cooking tamarind,” is available at Asian markets.
Whisk chiles, tamarind, brown sugar, salt, and 1 Tbsp. oil in a shallow baking dish until sugar is dissolved. Add steak and turn to coat. Cover and chill at least 4 hours.
Heat 2 tsp. oil in a large skillet over high heat. Working in 2 batches and adding remaining 2 tsp. oil between batches, cook steak until deeply browned, 2–4 minutes per side for medium-rare.
Transfer steak to a cutting board; let rest at least 5 minutes before slicing.
Steak can be marinated 1 day ahead. Keep chilled.