Get the mustard, Horseradish sauce, and mayonnaise together in a bowl

Mix it up and set aside.

Toast the bread

Add the Horseradish mixture to the bread

Add two slices of luncheon meat to the bread add the rest of the mixture to the third slice of toasted pumpernickel bread.

Stack the two slices of bread with the ham on it on top of each other.

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Add the top slice of bread with the Horseradish mixture on it