Pat dry steaks and salt generously on both sides; allow to stand on paper towels for 30-60 minutes before cooking.
In the meantime make a paste of the garlich by sprinkling a generous amount of course salt on top of the smashed garlic and using the palm of your hand on the flat side of a knife, slide the knife over the garlic repeatedly until a paste forms.
Pat the rested steaks dry and firmly press the top and bottom of each steak into the peppercorns.
Heat a large cast iron skillet over high heat. Add 2 tbsp of butter and 1 tbsp olive oil; melt butter, stirring to combine.
Gently place the steaks into the hot pan and sear over high heat for two minutes on each side. Don't move the steaks around. Allow to form a crust.
Reduce the heat to medium-low, add the remaining 3 tbsp of butter, garlic paste, thyme and rosemary. Continue cooking the steaks, turning occasionally and basting with the pan liquid, until your desired doneness is reached (about 8 minutes for medium).
Remove the steaks from pan and tent with foil to rest.
Discard the liquid from the pan, but do not scrape up any bits stuck to the bottom.
Place the pan over medium-high heat and add 1/3 cup cognac. Light the cognac with a match to burn off the alcohol. Whisk in the heavy cream, stirring frequently, until thickened, about 2 minutes. Pour in the juices that have accumulated on the plate from the steaks, along with 1 Tbsp of cognac. Quickly stir until thickened again, about 30 seconds.
Plate the steaks, topping them with a generous amount of sauce.