Pre-heat oven to 400F. Peel and slice your shallot. Mince the leaves of the rosemary sprig.
Rub steaks with 1 tablespoon of olive oil, salt and pepper. Set aside.
Add the other tablespoon of olive oil to the sauce pot, then add the shallots. Sauté until tender, approximately 4 minutes.
Add in rosemary, and stir well. Pour in the broth and bring to a simmer. Mix in the port wine and simmer until it reduces by half.
In the meantime, heat an oven-safe skillet the stove on medium-high heat. Once hot, place steaks in skillet.
Sear steaks for 2 minutes on each side, then pop it in oven (400F).
Turn off the oven, don't open the door, and set a timer for 4 minutes. Chop up chocolate, remove sauce from the heat, and whisk in the chocolate until it is melted and smooth.
Remove steak from the oven, and place on a cutting board to settle for 5 minutes.
Spoon the sauce on to your plates. Plate steak over the sauce.
