Preheat oven to 400 degrees. Prepare the sauce first, and keep warm over low heat.
In a medium sized skillet over medium-high heat, add the butter and once melted, add onion, garlic, de-seeded pasilla chile pieces and cook until the onions are soft and pliable.
Once the chiles are cooked and onions are soft, add chicken stock, brown sugar and torn tortilla pieces. Cook while stirring occasionally until the tortilla pieces are almost dissolved or quite soft. Remove from heat and let cool for the blender.
Add the chile sauce to a blender and process until you have a smooth sauce (about 3 minutes).
Run the sauce back into the skillet through a fine mesh sieve. Use a ladle or rubber spatula to press the sauce through. Once all of the sauce has been pushed through, take a rubber spatula and clean off the back side of the sieve to remove any stuck on sauce. Discard the contents in the sieve.
Bring the sauce back up to a simmering temperature and add heavy cream. Stir. At this point, the sauce can be adjusted with salt and pepper if it needs any. Reserve the sauce and keep warm.
Using a de-nuded or cleaned beef tenderloin, be sure to remove all silver skin or sinew. If you have a tenderloin with the tail end, cut this off and save for another meal (unless you need additional portions). Just be sure to fold the end of the tail end under before securing with butchers twine. How much you fold under depends on the amount you have. The idea is to fold the smaller end under itself to more or less equal the thickness of the rest of the cut of tenderloin.
Tie butchers twine in evenly spaced intervals as shown in the pictures. This will help the tenderloin hold a consistent shape and size.
Once the tenderloin is trussed or secured with twine, rub the tenderloin all over with olive oil. Add salt and pepper to coat the whole tenderloin.
Prepare a baking sheet with the cinnamon, coffee, cocoa, adobe seasoning mixture. Make sure this dry rub is thoroughly mixed. Add the tenderloin and roll into the rub to cover completely.
Lift the tenderloin out of the coffee mixture and tap to remove any excess seasoning. Place the tenderloin on a roasting pan or sheet pan and place into a 400 degree oven.
Roast the tenderloin for 10 minutes, then reduce the heat to 225-230 degrees. Continue roasting the tenderloin until the internal temperature reaches 130 degrees for medium rare, about 25-30 minutes. Cook the tenderloin more or less to the degree of doneness you wish.
Before carving, allow the meat to rest on a cutting board with an aluminum foil tent placed over top to keep warm.
Remove the strings from the tenderloin and slice the meat in 1/2 inch slices. Cut only enough meat you need to serve. Save the rest as backup if desired.
Serve on a warmed platter or dish with pasilla chile sauce.