In a medium bowl, whisk together 2 tablespoons of oil, 1 tablespoon of Sriracha, freshly ground pepper, and 2 tablespoons of soy sauce. Add the steak strips, ensuring they are well-coated with the marinade. Cover the bowl and let it sit at room temperature for at least 30 minutes.

Heat a cast iron skillet over medium-high heat until it’s hot enough that a drop of water sizzles upon contact. Add 1 tablespoon of butter, letting it melt and foam, then season the marinated steak strips generously with salt. Sear the steak for 1–2 minutes on each side until golden brown and crusty.

Remove the steak from the skillet and set it aside on a plate to rest. Lower the heat slightly and add 2 more tablespoons of butter to the skillet. Let it melt, and then sauté 1 chopped shallot and 2 minced garlic cloves for about 2 minutes.

Add 1 teaspoon of dried thyme, chopped chives, and a pinch of chili pepper flakes to the skillet. Stir in the juice of half a lemon, 1 tablespoon of Dijon mustard, and 1 cup of beef stock. Simmer gently for about 5 minutes, allowing the sauce to reduce by half and thicken slightly.

Return the seared steak strips to the skillet and gently coat them in the sauce. Simmer for an additional 1–2 minutes. Taste the sauce and adjust the seasoning as needed.

Transfer the steak to a serving plate, drizzling the buttery sauce over the top. Garnish with fresh parsley and additional chives.