Remove steaks from the fridge and season all sides with cocoa rub (about 1 tablespoon per steak).
Let the steaks rest 30 – 45 minutes on the counter prior to cooking so the meat comes closer to room temperature.
Add 1 tablespoon of high smoking point cooking oil (canola works fine) to a seasoned cast-iron skillet and turn the burner to medium-high heat.
Warm the oil until the surface just begins to shimmer (that's how you know it's hot enough to sear).
Place steaks into the hot pan (it should sizzle). Make sure not to crowd the pan. If you're cooking more than 2 or 3 steaks you may need to use two pans.
Let the steaks cook for 3 minutes. Flip the steaks over, then let them cook another 3 minutes. We recommend using a timer here. If you want to sear the sides, cook them for about 30 seconds on each side using your tongs to hold up each steak.
Using an oven mitt, transfer the pan to the oven and let it cook for 4-5 more minutes. This will create a medium, pink center. If you want it medium rare or rare, try 2-4 minutes.
IMPORTANT: For smaller, leaner steaks you'll want to keep it in the oven no longer than 2 minutes, even less if you want to achieve medium rare. For a larger, fattier cuts, 4-6 minutes will achieve a pink center. And if you're uncertain, you can always do the finger test to check for doneness. Do however, take the steaks out of the oven prior to desired doneness as they will continue to cook away from the heat for a minute or so.
Remove pan from the oven. Using tongs, place the steaks on a cutting board or plate, cover loosely with aluminum foil or a dish towel and let rest for 7-10 minutes without cutting into them.
Cut into ½” to 1” strips.
A few minutes before serving, when you plate the meat, top the steak with whisky gravy.
For the Whisky Gravy
In a medium skillet, melt 3 tablespoons butter and cook the onions until soft and translucent.
Turn off the heat and whisk in the whisky and vanilla bean seeds. As soon as the fumes evaporate, turn on burner to medium. If whisky ignites, remove from heat and let it burn off briefly, cover to extinguish flame, and carefully return to the burner.
Whisk in the beef stock, salt and pepper. Cook over medium heat until liquid is reduced by half.
Whisk in the cream, lower the heat to simmer, and cook until thickened. Add the last tablespoon of butter and whisk until melted.
