Combine the softened butter with the minced garlic, chopped parsley, lemon zest and kosher salt in a medium bowl.
Use a hand mixer or a rubber spatula to stir to combine.
Roll into a log or transfer to a storage container to keep the butter in the refrigerator. This can be kept for 2-3 week in the fridge. You may also leave at room temperature if you’re cooking the steak shortly after mixing it.
Cook the Sirloin Steaks
About 30-45 minutes before cooking, remove the steaks from the fridge and let them come to temperature.
Warm a cast iron skillet over high heat. (You want it screaming hot because this will get a good sear and caramelization on the outside of the steak, which provides both flavor and texture.)
As the cast iron skillet heats, season the steak with salt and pepper on all sides.
Place the steak in the middle of the skillet dry. Do not add the butter yet, and do not overcrowd the pan.
Sear the steak for 4 minutes, then flip and cook for another 2. This will get you close to rare or medium rare, depending on the thickness of your steak. If the steak has a fat cap, be sure to sear this part, too, for a few minutes so it caramelizes.
Lower the heat to medium and add 2 tablespoons of the garlic butter per steak. Baste for another 2-3 minutes, or until the steak reaches your ideal temperature.
Remove the steak from the pan, and let rest for 10-15 minutes under foil.
Serve with another tablespoon of the garlic butter, and enjoy with your favorite sides!
The cook times will vary based on the thickness of the steak, as well the temperature you like to eat your steak. Steak temperatures: Rare (cool red center): 125°F
Medium rare (warm red center): 135°F
Medium (warm pink center): 145°F
Medium well (light pink center): 150°F
Well done (cooked entirely through): 160°F