1 medium (8-ounce; 225g) yellow onion, peeled and halved crosswise
1/4 cup (60ml) vegetable oil
1/4 cup (60g) double-concentrated tomato paste
1/4 cup (60ml) red wine
1 tablespoon (9g) Diamond Crystal kosher salt; for table salt, use half as much by volume or the same weight
1/2 teaspoon freshly ground black pepper
2 pounds (900g) boneless beef flap meat or lamb leg, trimmed of excess external fat, silver skin, and tough sinew, and cut into 1-inch wide by 1/2- to 1-inch-thick pieces (see note)
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