In a small mixing bowl, combine the softened butter, minced garlic, chopped fresh parsley, chopped fresh thyme, red pepper flakes (if using), and salt. Mix thoroughly with a fork or whisk until all ingredients are well incorporated. Set aside at room temperature.

Pat the skirt steak pieces very dry with paper towels. This is crucial for achieving a good sear. Season both sides generously with kosher salt and freshly ground black pepper.

Heat a heavy-bottomed cast iron skillet over high heat until it just begins to smoke lightly, about 3-5 minutes. Add the olive oil to the hot pan and swirl to coat.

Carefully place the skirt steak into the hot skillet. Sear for 2-3 minutes per side for medium-rare, or 3-4 minutes per side for medium. Adjust cooking time based on steak thickness and your desired doneness. Skirt steak cooks quickly.

During the last minute of cooking, add half of the prepared garlic herb butter to the skillet. As it melts, tilt the pan slightly and use tongs or a spoon to baste the steak with the melted butter. Flip the steak and baste the other side briefly.

Remove the steak from the skillet and transfer it to a cutting board. Immediately spoon the remaining fresh garlic herb butter over the hot steak. This allows the butter to melt and further infuse the steak as it rests.

Let the steak rest for at least 5-10 minutes before slicing. Resting allows the juices to redistribute, ensuring a tender and moist steak. Tent loosely with foil if desired.

Slice the skirt steak against the grain into thin strips. Serve immediately, drizzling any accumulated pan juices and melted garlic butter over the sliced steak.