Heat up a heavy-walled 10-12 inch aluminium skillet over a medium-high flame. Sear the steak, on both sides. Test it for doneness by poking it. It should put up some resistance. Remove the steak from the pan.
Add 1 Tbl of butter to the pan. Throw the sliced onion in. Season with salt and sweat the onions down. Add the tomato paste and continue sauting until the paste is slighly caramelized. Turn off the flame. Add the Cognac and stand back. Ignite the Cognac with a long match or a firestick. Allow the towering inferno of flames to die down. Turn the flame back on. Throw in the wine and cayenne pepper. Scrape the bottom of the pan to liberate all the gripped-on residue. Reduce the liquid over a medium-low flame. Pour any accumulated juices, exuded from the steak back into the pan. When the liquid is reduced by half, add the heavy cream. Reduce this until the sauce coats the back of a spoon. Adjust for seasoning with black pepper. Immerse the steak into the pan sauce.