Preheat oven to 425 degrees F.
Heat a small skillet over medium heat. Add oil, butter, shallot and chopped mushrooms. Season mushrooms with salt and pepper and saute 5 minutes. Add sherry to the mushrooms and let the liquid evaporate. Remove mushrooms from the heat.
In a nonstick skillet over high heat, sear meat 2 minutes on each side in a drizzle of oil. Remove skillet from the heat and season meat with salt and pepper.
Cut mousse into 4 pieces, 2 ounces each sliced in 1/2 horizontally. Spread the puff pastry sheet out on to a cookie sheet covered with parchment paper. Quarter the dough with a sharp knife. Roll each piece of dough into a 10 by 6-inch rectangle. On each rectangle of dough, place 1/4 of the cooked mushrooms. Top mushrooms with 2 ounces pate and 1 tournedo of beef. Wrap dough up and over the meat. Seal the dough with egg wash and trim excess. Use leftover dough bits to make decorative garnishes for the tops of your Wellingtons. Turn the wrapped Wellingtons over and cover with egg wash using a pastry brush. Affix dough garnishes with egg wash. For a simple decoration, roll dough bits into a long, thin spaghetti like string and make swirls on each Wellington. Bake beef Wellingtons 10 minutes or until golden. Let stand 5 minutes, then serve.
Steam broccoli spears in 1-inch simmering salted water, covered, for 8 to 10 minutes, or until just tender. Transfer spears to a serving plate or individual dinner plates along side Wellingtons.