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1
Slice the loaf of bread in half and hollow out a lot of the crumb to make room for the sandwich fillings.
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2
Slice the mushrooms finely and dice the shallots. Heat the butter and cook the mushrooms and shallots over medium heat with a generous grinding of salt and pepper. When the mushrooms start to release their juices, add the madeira and Worcester sauce and keep cooking until all of the liquids have evaporated.
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3
Meanwhile, salt and pepper the steaks. Heat a large cast iron skillet and sear the steaks on both sides until they are cooked to medium.
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4
While the ingredients are still hot, assemble the sandwich. Mix the creamed horseradish and mustard and slather half on one of the steaks. Place this, horseradish down, into a carved out bread half. Layer on the mushroom mixture and then the chopped parsley. Layer on the second steak, slather with the remaining horseradish mixture, and layer on the top half of the bread loaf.
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5
Wrap the sandwich in plastic wrap, followed by aluminum foil, and weigh down overnight in the refrigerator under heavy weights, such as a cast iron skillet with canned tomatoes. Remove from the refrigerator for several hours before serving, to bring to room temperature. When you are ready to serve, unwrap the sandwich, slice, and serve.
