Beef Wellington With Mushroom Pate

In food processor using pulsing motion, process mushrooms until finely chopped. Set aside.

In 12" skillet over medium-high heat, melt margarine; add onion; cook 3 to 4 minutes, stirring frequently until softened. Add mushrooms; cook 10 minutes, stirring frequently and scraping bottom of skillet until liquid has evaporated and mushrooms are dry. Remove from heat; stir in parsley, thyme, salt and pepper. Transfer mixture to large plate; flatten with spoon. Refrigerate 10 minutes until cool.

Meanwhile, using sharp knife, even off diameter of beef tenderloin by cutting off large piece of meat protruding from side of tenderloin. Set both pieces aside, reserving cut-off piece for stir-fry or beef stew.

Unfold one pie crust onto lightly floured surface; brush all over with 1 teaspoon water. Unfold second pie crust on top of first; roll out to 15x12" rectangle. Turn crust so one long side faces you; spoon cooled mushroom mixture in even strip across center of crust, covering area the size of beef tenderloin. Place tenderloin on top of mushroom mixture.

In small bowl using fork, beat egg yolk and remaining 1 teaspoon water to blend; brush some of mixture along edges of crust rectangle. Fold crust over beef, overlapping edges and turning in ends; press with fingertips to seal. Place tenderloin, seam side down, on lightly greased large rimmed cookie sheet; brush all over with more of yolk mixture. Place in freezer 10 minutes.

Meanwhile, heat oven to 375 degrees F.

Roast tenderloin 50 to 60 minutes until meat thermometer inserted in thickest part registers 140 degrees F for rare. Remove from oven; let stand 10 minutes.

Using large metal spatulas, carefully transfer tenderloin to serving platter; serve garnished, if desired, with herb sprigs.