STUFFING: Puree the mushrooms and onions together in a food processor. Meltthe butter in a skillet over medium heat, add the mushroom and onionmixture and cook, stirring occasionally, until the mixture is dry. Add saltand pepper to taste and mash in the pate. Transfer the stuffing to a bowland chill in the refrigerator.
MEAT: Heat the oil in a skillet over high heat. Add the beef and sear onall sides. Remove the beef from the skillet and sprinkle with salt andpepper. Place in the refrigerator until cold.
ASSEMBLE THE WELLINGTON: Roll out chilled puff pastry into a rectanglelarge enough to enclose the beef. Spread the dough with a generous layer ofstuffing, place the beef on top and spoon another bit of stuffing on thebeef. Wrap the pastry to enclose the beef and stuffing and place theWellington in the refrigerator to chill for at least 15 minutes.
COOK THE WELLINGTON: Preheat oven to 220ºC . Place Wellington in oven andimmediately lower heat to 180ºC . Roast for about 20 minutes.