- a trimmed 4 1/2- to 5-pound beef tenderloin roast (about 16 inches long and 3 inches in diameter)
- 1 tablespoon vegetable oil
- 1 large egg
- 1 tablespoon water
- Sour Cream Pastry Dough
- Coriander Walnut Filling
- Trim tenderloin if necessary and pat dry. Halve tenderloin crosswise and season with salt and pepper. In a large heavy skillet heat oil over moderately high heat until just smoking and brown beef, 1 piece at a time, on all sides, about 2 minutes total for each piece of beef, transferring to a platter.
- Make an egg wash by lightly beating egg with water. On a lightly floured surface with a floured rolling pin roll out dough into a 19- by 15-inch rectangle (slightly less than 1/4 inch thick). Cut a 1-inch strip of dough from a shorter end (leaving an 18- by 15-inch rectangle) and reserve strip. Arrange rectangle lengthwise on a baking sheet or tray (about 17 1/2 by 12 1/2 inches), letting excess hang over. Spread one third filling lengthwise down middle of rectangle, forming a 16- by 2-inch strip. Arrange beef pieces end to end lengthwise on filling and spread remaining filling on top of beef. Brush edges of dough with some egg wash. Fold up long sides of dough to enclose beef completely and seal edge. Fold ends of dough over wrapped beef and seal edges. Invert a large baking sheet onto wrapped beef and invert beef onto sheet so that pastry is seam side down. Brush crust evenly with some egg wash. Cut out holly leaves and berries from reserved pastry strip and arrange on crust, gently pressing to make them adhere. Brush decorations with some egg wash and with a sharp knife make small steam vents every 3 inches on top of crust. Chill beef en croûte, loosely covered, at least 1 hour and up to 6.
- Preheat oven to 400°F.
- Bake beef en croûte in middle of oven 45 minutes, or until pastry is golden brown and a thermometer inserted diagonally 2 inches into center of beef registers 115°F. Let beef stand on sheet on a rack 25 minutes. Beef will continue to cook as it stands, reaching 125°F. (medium-rare).