3-4 lb. beef tenderloin, trimmed of fat
1 tsp. salt, divided
1 tsp. pepper, divided
1/2 cup butter
1 lb. fresh mushrooms, chopped
4 green onions, finely chopped
1 sheet frozen puff pastry, thawed
1 egg yolk
1 tsp. water
Preheat oven to 400 degrees.
Rub beef with 1/2 tsp. each of salt and pepper. Cook beef in roasting pan 25 to 30 minutes or until a meat thermometer inserted in center of meat registers 120 degrees. Cool to room temperature.
Reduce oven temperature to 350 degrees.
In a medium skillet melt butter over medium-high heat. Stir in mushrooms, onions and remaining salt and pepper. Saute 2 to 3 minutes or until onions are soft.
On a lightly floured surface, use a floured rolling pin to roll out pastry to a 10x13" rectangle (or large enough to wrap completely around beef). Mix egg yolk and water in a small bowl. Spread mushroom mixture evenly on rolled pastry to within 2" of each edge. Center beef on pastry. Fold pastry around beef and seal edges with egg yolk. Place beef, seam side down, on a greased baking sheet. Brush top of pastry with egg yolk. Using dough scraps (or another sheet of dough) cut shapes for garnish (stars, hearts?). Arrange cut-outs on top of pastry; brush with remaining egg yolk.
Bake 25 to 30 minutes or until meat thermometer registers 130 degrees. If pastry browns too quickly cover with foil. Cool 10 minutes. Slice to serve.
