Steak Tacos with Sweet and Spicy Pickled Onions

Sweet and Spicy Pickled Onions
1 medium red onion, sliced thin (about 1 1/2 cups)
1 cup red wine vinegar
1/3 cup sugar
2 jalapeño chiles, stemmed, seeded, and cut into thin rings
1/4 teaspoon table salt

Herb Paste
1/2 cup packed fresh cilantro leaves
3 medium garlic cloves, roughly chopped
3 medium scallions, roughly chopped (about 1/3 cup)
1 medium jalapeño chile, stemmed and roughly chopped (see note)
1/2 teaspoon ground cumin
1/4 cup vegetable oil
1 tablespoon fresh lime juice

1 flank steak (1 1/2 to 1 3/4 pounds), trimmed of excess fat and cut lengthwise (with grain) into 4 equal pieces
1 tablespoon kosher salt or 1 1/2 teaspoons table salt
1/2 teaspoon sugar
1/2 teaspoon ground black pepper
2 tablespoons vegetable oil

12 6-inch corn tortillas, warmed
Fresh cilantro leaves
Minced white or red onion
Lime wedges

1. FOR ONIONS: (The pickled onions can be refrigerated in an airtight container for up to 1 week.) Place onions in medium heat-resistant bowl. Bring vinegar, sugar, jalapeños, and salt to simmer in small saucepan over medium-high heat, stirring occasionally, until sugar dissolves. Pour vinegar mixture over onions, cover loosely, and let cool to room temperature, about 30 minutes. Once cool, drain and discard liquid.

2. 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.

3. 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.

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.

5. FOR THE TACOS: Using sharp chef’s knife or carving knife, slice steak pieces across grain into 1/8-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.

Technique: How to Warm Tortillas
Toast them in a dry skillet over medium-high heat until softened and speckled with brown spots, 20 to 30 seconds per side. You can also use the oven: Divide the tortillas into 2 stacks and wrap each stack in foil. Heat the tortillas on the middle rack of a 350-degree oven for 5 minutes.