In a food processor, add vinegars, garlic, capers, shallots, herbs and dijon. Process while slowly adding olive oil until creamy.
Season tenderloin with salt and freshly ground pepper. In a large fry pan over high heat add a little oil and sear tenderloin on each side for 10 seconds. Remove from heat and roll in marinade. Set aside and allow to cool.
Wrap marinaded beef in plastic wrap and twist ends to make a tight cylindrical shape. Refrigerate for at least 1 hour.
In a food processor or in a bowl with a whisk mix together crème fraiche, horseradish and grainy mustard. Season with a little salt and refrigerate until ready to use.
Thinly slice pumpernickel bread. Spread with a little butter and put aside. Remove plastic wrap from beef and slice no thicker than 1/16 inch. Place on top of bread and spoon over a little horseradish cream. Serve immediately.