|½||cup packed fresh cilantro leaves|
|3||medium garlic cloves, roughly chopped|
|3||medium scallions, roughly chopped (about ⅓ cup)|
|1||medium jalapeño chile, stemmed and roughly chopped (see note)|
|½||teaspoon ground cumin|
|¼||cup vegetable oil|
|1||tablespoon fresh lime juice|
|1||flank steak (1½ to 1¾ pounds), trimmed of excess fat and cut lengthwise (with grain) into 4 equal pieces (see below)|
|1||tablespoon kosher salt or 1½ teaspoons table salt|
|½||teaspoon ground black pepper|
|2||tablespoons vegetable oil|
|12||(6-inch) corn tortillas, warmed (see note)|
|Fresh cilantro leaves|
|Minced white or red onion|
1. FOR THE HERB PASTE: Pulse cilantro, garlic, scallions, jalapeño, and cumin in food processor until finely chopped, ten to twelve 1-second pulses, scraping down sides as necessary. Add oil and process until mixture is smooth and resembles pesto, about 15 seconds, scraping down sides of workbowl as necessary. Transfer 2 tablespoons herb paste to medium bowl; whisk in lime juice and set aside.
2. FOR THE STEAK: Using dinner fork, poke each piece of steak 10 to 12 times on each side. Place in large baking dish; rub all sides of steak pieces
evenly with salt and then coat with remaining herb paste. Cover with plastic wrap and refrigerate at least 30 minutes or up to 1 hour.
3. Scrape herb paste off steak and sprinkle all sides of pieces evenly with sugar and pepper. Heat oil in 12-inch heavy-bottomed nonstick skillet over medium-high heat until smoking. Place steak in skillet and cook until well browned, about 3 minutes. Flip steak and sear until second side is well browned, 2 to 3 minutes. Using tongs, stand each piece on a cut side and cook, turning as necessary, until all cut sides are well browned and internal temperature registers 125 to 130 degrees on an instant-read thermometer, 2 to 7 minutes. Transfer steak to cutting board and let rest 5 minutes.
4. FOR THE TACOS: Using sharp chef’s knife or carving knife, slice steak pieces across grain into ⅛-inch-thick pieces. Transfer sliced steak to bowl with herb paste-lime juice mixture and toss to coat. Season with salt. Spoon small amount of sliced steak into center of each warm tortilla and serve immediately, passing toppings separately.