Chop the mushrooms in a food processor, not too small.
Saute the chopped mushrooms, shallots, and sherry in the butter. Cook until the mushrooms have given up their juice and most of it has evaporated. Set aside until cool.
For the Roast
Trim the steak of unwanted fat. Lay the steak flat and pound it with the meat hammer so it is all about the same thickness. You want to do this for even heating.
Put the spinach, duxelles, and blue cheese on top. Roll the steak up and secure it with butcher's twine.
Combine the rub ingredients and spread them out on a cutting board. Roll the flank steak in the rub, pressing hard. After rolling all the sides, take a meat hammer and pound the seasonings in further.
Roast, covered, at 350 F/ 176 C for 20 minutes per pound or until an instant-read thermometer reads 130 F/ 54 C.
Let the roast rest for 10-15 minutes then remove the twine.
Slice and serve. Enjoy!
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