Combine creme fraÂŒche, mustard, tomato paste, Worcestershire sauce, paprika, salt, pepper to taste, and demiglace in a medium-size saucepan and simmer slowly for 20 minutes, or until sauce is slightly reduced. Remove from heat and let stand, covered, while completeing recipe. Trim stem ends off mushrooms and discard. Wipe mushrooms with a damp paper towel and slice thin. Melt 3 tablespoons of butter in a medium sized skillet and saut, mushrooms until tender and golden, about 10 minutes. Transfer to a bowl and reserve. Cut a small X in the root end of each pearl onion. Bring a large kettle of water to a boil and drop in the onions. Blanch for 10 minutes, drain, and rinse under cold running water. Peel the onions. Heat another 2 tablespoons of butter in the same skillet and saut, the onions, stirring and shaking the skillet often, until they are lightly browned, 3 to 4 minutes. Transfer the onions to the bowl with the mushrooms. Cut the meat into thin slices on the diagonal. Heat remaining butter in the skillet and saut, the pieces of filet over high heat until just lightly browned. Transfer pieces to a plate as each batch is browned. Recipe can be prepared to this point several hours before serving. To complete, set sauce over medium heat and bring to a simmer. Add mushrooms, onions and any accumulated juices from the bowl, and simmer for 5 minutes. Add slices of filet and any accumulated juices and simmer until the meat is heated through, about 2 minutes. Serve immediately over buttered noodles. Garnish with chopped parsley. Garnish side with saut, ed cherry tomatoes and pour a good red wine.