Preheat oven to 200F
Pat the steak dry and coat with the salt and pepper.
Next, heat up a cast iron skillet over high heat and add the butter. Once the butter begins to melt, place the steak in the butter and sear for 4-5 minutes.
Flip the steak and cook another 4-5 minutes (time may vary slightly depending on the thickness of your steak and desired doneness). For medium-rare, the meat thermometer should read 135.
When finished searing the steak, place the steak on a heat proof pan or plate and place into the warm oven.
Next, return your skillet with the steak drippings to the stovetop over medium heat.
Add the cognac, garlic, and rosemary and reduce until about ⅓ of the liquid is left and it becomes glossy, about 5 minutes.
Add the heavy cream, whole green peppercorns, and salt and whisk to combine. Allow the mixture to simmer, whisking occasionally, and let reduce by about half, approximately another 5 minutes.
Turn the heat off and whisk in the 1 tablespoon of butter. Strain the sauce (optional) and top the steak with it. Serve immediately.
