Pat the steak dry with paper towels and season with salt. Coarsely crush the peppercorns in a mortar and pestle or alternatively, place the peppercorns in a small resealable bag and crush them with a meat mallet or the bottom of a cast iron skillet.
Spread the peppercorns on a plate then, press the crushed pepper onto both sides of each steak evenly.
Add the oil and 1 tablespoon of butter to a large skillet (cast iron work well), and heat over medium-high heat. When the oil is hot and shimmering, place the steaks in the pan and cook undisturbed for about 4 minutes or until a nice golden crust has formed. Flip the steak to cook the other side.
Optional: Lower the heat to medium and add the garlic and fresh rosemary. With a spoon, baste the steak pouring the oil butter mixture over it.
Cook for about 3-4 minutes for medium-rare (135ºF) removing the steak from the pan when it reaches an internal temperature of 130ºF when checked with an instant-read thermometer. (please see chef's notes). Transfer the steak to a plate or cutting board to rest, tented with aluminum foil.
Pour off any excess fat but don’t wipe the skillet clean. Lower the heat to medium-low and add the remaining butter. As soon as the butter melts, add the shallots. Cook the shallots, stirring constantly with a wooden spoon, scrapping up the brown bits until the shallots become soft, about 2 - 3 minutes.
Off the heat, pour the cognac and return the skillet to the stove (be careful it may ignite) and boil once again scrapping up the brown bits stuck at the bottom. Cook until the liquid is mostly absorbed by the shallots and reduced to a glaze.
Stir in the heavy cream and bring to a gentle boil, stirring frequently until thickened to sauce consistency, about 4 minutes. Season with salt to taste and stir in any meat juices that accumulated on the plate.
Transfer the steaks to serving plates and serve with sauce pour on top. Garnish with chopped parsley or thyme leaves (optional). Serve immediately.