In a small bowl, combine the softened butter, minced garlic, chopped fresh parsley, chives, thyme, lemon zest, salt, and pepper. Mix thoroughly until all ingredients are well incorporated. Set aside at room temperature, or refrigerate if making ahead (bring to room temperature before use).

Pat the skirt steak very dry on all sides with paper towels. This step is crucial for achieving a good sear. Trim any excess silver skin or tough membrane from the steak.

Lightly rub both sides of the steak with olive oil, then season generously with kosher salt and freshly ground black pepper.

Heat a large cast-iron skillet over high heat until it just begins to smoke, about 3-5 minutes. The skillet needs to be very hot for a proper sear.

Carefully place the seasoned skirt steak in the hot skillet. Cook for 2-4 minutes per side for medium-rare (internal temperature 130-135°F / 54-57°C). Adjust cooking time for your desired doneness: 2 minutes per side for rare, 3-4 minutes per side for medium, 4-5 minutes per side for medium-well. Use tongs to flip the steak.

During the last minute of cooking, add about half of the prepared garlic herb butter to the skillet. As it melts, tilt the pan slightly and continuously baste the steak with the melted butter using a spoon.

Remove the steak from the skillet and transfer it to a clean cutting board. Immediately place the remaining garlic herb butter on top of the hot steak.

Let the steak rest for 5-10 minutes before slicing. Resting allows the juices to redistribute throughout the meat, resulting in a more tender and flavorful steak.

Slice the skirt steak thinly against the grain. Serve immediately, drizzling any accumulated melted garlic butter from the cutting board over the sliced steak.