Instructions: Trim fat from tenderloin. Rinse meat, pat dry, and fold tip under to make roast evenly thick. Tie at 2-inch intervals with cotton string. Rub with olive oil and sprinkle with salt and pepper.

In a 10- to 12-inch ovenproof nonstick frying pan over high heat, turn meat to brown all sides, about 4 minutes total.

Put pan with meat in a 450 degree oven. Bake until a thermometer inserted into center of thickest part reads 150 degrees, 5 to 8 minutes. Let cool 20 minutes; cover and chill until cold, at least 1 hour.

Trim and discard tough stems from mushrooms; rinse caps and finely chop. In a 10- to 12-inch frying pan over medium-high heat, frequently stir mushrooms, sake, shallots, and butter or olive oil until mushrooms are lightly browned, about 10 minutes. Let cool, about 20 minutes.

Unfold puff pastry. Cut a 1/2-inch-wide strip off 1 edge and reserve. Roll pastry into a neat rectangle 1 1/2 inches longer than the roast and 1 1/2 inches wider than its circumference.

Gently pat mushroom mixture over pastry up to 1 inch from edges. Pat pork dry and remove string. Center roast lengthwise on pastry. Brush pastry edges with water. Using both hands, quickly lift 1 long side over meat. Repeat to lift opposite side over meat; press edges together to seal. Fold in pastry ends, overlapping to cover ends of roast; press firmly to seal. Set roast seam down in an oiled rimmed 10- by 15-inch pan.

On floured board, roll reserved pastry strip 1/8 inch thick. With the tip of a sharp knife or flour-dusted cookie cutters, cut out decorative shapes, such as leaves. Brush a little water onto 1 side and arrange on roast, moistened-sides down; press gently to hold in place.

In a small bowl, beat egg yolk to blend with 1 tablespoon water. Brush mixture over pastry.

Bake Wellington in a 400 degree oven until pastry is richly browned, 25 to 30 minutes. With 2 wide spatulas, transfer roast to a platter. Let rest 15 to 20 minutes. Garnish with watercress. Cut roast crosswise into 1-inch-wide slices.

As meat bakes, make sauce. In a 10- to 12-inch frying pan, combine shallots, vinegar, sake, and whipping cream. Boil over high heat, stirring often, until reduced to 1/2 cup, 8 to 10 minutes. Serve hot.

This recipe yields 4 servings.

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