Grilled Flank Steak with Charred Lemon Chimichurri

1 small lemon

1 small jalapeño

½ cup extra-virgin olive oil, plus additional for tossing ingredients and oiling the grill

1½ teaspoons kosher salt, divided

1 cup lightly packed flat-leaf parsley leaves

1 cup lightly packed fresh cilantro leaves

3 tablespoons fresh oregano leaves

2 cloves garlic, coarsely chopped

1 tablespoon coarsely chopped shallot

1 tablespoon white wine vinegar

 

1 flank skirt or flatiron steak (about 1½ pounds)

Kosher salt and freshly ground black pepper

 

To make the chimichurri, trim the blossom and stem ends of the lemon, removing enough rind that the pulp shows. Cut the lemon into ¼-inch-thick slices and put them in a small bowl with the jalapeño. Toss with a little bit of oil and ¼ teaspoon of the salt, and grill or broil until lightly charred. Put the lemon slices and jalapeño back in the bowl and cover with a plate or plastic wrap. The steam will cause them to collapse slightly, making the skin of the jalapeño easy to remove. Peel and seed the jalapeño (leave some seeds and the membrane if you want a spicy kick). Remove any seeds from the lemon slices. Put both ingredients in the bowl of a food processor and pulse several times to coarsely chop. Add the remaining 1¼ teaspoons salt, the parsley, cilantro, oregano, garlic, shallot, and vinegar. Pulse the ingredients in short bursts, to chop and combine them without creating too fine a puree. With the motor running, drizzle in the oil. Remove the sauce to a medium bowl and let it sit for at least 2 hours or up to overnight.  Taste for salt before serving, adding more if necessary. Pat the steak dry with a paper towel and season it generously with salt and pepper. Preheat a gas grill for high heat, about 450 degrees F, or prepare a charcoal grill for direct-heat cooking over red-hot coals. Scrape the grate clean and lightly oil it. When the grill is hot, lay the steak on the grate. For rare to medium rare, cook for 3 minutes on one side, flip the steak, and cook for an additional 3 minutes on the other side (this may vary, depending on the size and thickness of the steak). Remove the steak from the grill and let it rest for at least 5 minutes before thinly slicing it against the grain. To serve, lay the slices on a platter, drizzle them with any juices left over from slicing, and spoon some chimichurri over the top. Serve immediately and pass remaining chimichurri.