Rub the coarse salt into the skirt steak and let rest for 15 minutes on a plate (this helps tenderize this cut of meat).
In the meantime, dry roast your aji panca chili pepper in a cast iron skillet on high heat, until pepper starts to blister (a few minutes).
Remove aji from skillet, place in a bowl and add boiling water to cover. Let sit for a few minutes. Once softened, cut lengthwise, deseed and devein (unless you like it really hot). Combine 1/4 cup of beef stock, chili, and Nutella and blend in food processor or blender. Set aside.
Shake/rub the salt off your steak and brush with 1 tablespoon olive oil, then season with black pepper. Grill or pan sear in a hot pan (depending on thickness, approximately 2-3 minutes a side for medium).
Once grilled to your liking, remove from pan and set to rest on a plate to catch all of the drippings (tent to keep warm). Deglaze your pan using the Jerez (sherry), olive oil, beef drippings and 3/4 cup of beef stock. Add flour to the pan and whisk to combine. Stir constantly for about a minute. To this, add the Nutella/panca chile liquid, coffee and cacao. Whisk to combine until desired thickness is reached.
Sprinkle dash of oregano, stir. Finally, add butter to give your sauce a lovely gloss.
Cut your steak across the grain, plate and spoon some of the steak sauce on top.