Generously season the steak and let it sit at room temperature for 30 minutes. Meanwhile, put the parsley, basil, garlic, capers, anchovies and Piment d'Espelette in a food processor or blender (a blender will produce a smoother sauce; I prefer a coarser sauce—either is fine. Go your own way!). Add a pinch of salt. Pulse the mixture until the leaves are broken down. With the machine running, begin adding the oil in a slow steady stream. If you like a dense green sauce, 1/2 cup of oil will do—if you want it to be looser, then keep adding oil. Add half the lemon juice and taste. Add more lemon, salt, or Piment d'Espelette to taste—I like the sauce to have a spark of heat but not be hot.
Set an oven rack 4 to 5 inches from the broiler flame, then heat the broiler. I like to broil the steak in a cast-iron pan, but you can use a baking sheet or broiler pan—whatever you have. Broil the steak for 3 minutes per side for medium rare (if your broiler is weak you may need 4 minutes per side). Transfer the steak to a cutting board and let rest for 5 minutes. Thinly slice the steak across the grain. Serve on a big platter, passing a bowl of lemon wedges and a bowl with the green sauce.
Before starting Food52 with Merrill, I was a food writer and editor at the New York Times. I've written several books, including "Cooking for Mr. Latte" and "The Essential New York Times Cookbook." I played myself in "Julie & Julia" -- hope you didn't blink, or you may have missed the scene! I live in Brooklyn with my husband, Tad, and twins, Walker and Addison.