Step 1

Pat the skirt steak dry with paper towels. Cut it crosswise into 3 equal pieces. Season all over with 1½ teaspoons kosher salt. Transfer to a shallow bowl or baking dish.

Step 2

Finely grate 2 garlic cloves into a glass measuring cup. Add red wine vinegar, sugar, smoked paprika and olive oil and whisk to combine. Pour half of that marinade over the steak, turning to coat. Let sit at least 15 minutes at room temperature or up to 4 hours in the refrigerator.

Step 3

Add the shallot, chile and roasted red peppers to the remaining marinade. Season with salt.

Step 4

Preheat a dry 12-inch cast-iron skillet over medium-high heat for at least 4 minutes to be sure it's nice and hot right off the bat (this steak cooks super quickly). You should be able to see some very light wisps of smoke coming off the pan.

Step 5

Remove the steak from the marinade, allowing any excess liquid to drip back into the bowl. Pat dry with paper towels.

Step 6

Working in 2 batches, add 1 tablespoon olive oil to the pan, allow it to heat up for about 30 seconds, then add half the steak and cook, undisturbed, until charred on the underside, 2 to 3 minutes. Flip and cook 1 minute on the second side. Transfer to a cutting board to rest for 5 minutes.

Step 7

Look at the steak and figure out which way the grain is running (i.e., which way the muscle fibers run). Thinly slice crosswise against the grain, perpendicular to the fibers. Not sure what the grain is or how to find it? Right this way. Transfer to a platter along with any juices on the cutting board (that's flavor — don't leave it behind). Spoon some of the chimichurri over the steak and serve the remainder alongside. Season with flaky sea salt.