assemble the sandwich!

cut the bread like a soup bowl, then hollow it out (save the center for bread crumbs or soup). place a steak on the bottom, then most of the mushrooms/shallots (add parsely for added awesome), then another steak, then some horseradish spread, spread some mustard on the 'lid', pour in the remaining duxelle (the mushroom/shallot mixture) and then put the lid on.

Done