Beef Wellington is a very impressive holiday main dish, yielding ultra-tender meat that you can cut with a fork, prettily wrapped in crisp puff pastry. Using an instant read thermometer makes this special cut of meat virtually impossible to overcook, and this recipe takes advantage of carryover heat to let the meat reach the perfect temperature.In the bowl of a food processor, pulse onion until very finely chopped. Transfer to a bowl. Place mushrooms in the food processor and pulse until very finely chopped. (Alternately, onion and mushrooms can be chopped very finely with a knife.)

In a large nonstick skillet, melt butter over medium-high heat. Add onions and sauté for 3 to 5 minutes, stirring occasionally, until softened. Add mushrooms, garlic, and salt. Turn heat down to medium and cook, stirring occasionally, until all of the liquid from the mushrooms have evaporated and mixture starts to brown, 15 to 20 minutes. Add sherry and stir until evaporated, about 30 seconds. Remove skillet from heat and stir in the rosemary. Let cool for 10 minutes (or refrigerate up to 1 day).
Lay the tenderloin on a parchment-lined baking sheet. In a small bowl, mix together the Dijon, salt and pepper, then spread all over the meat. Cover with plastic wrap and refrigerate.

On a piece of parchment paper, roll puff pastry into a 10-inch by 11-inch rectangle. Use a pastry brush to brush the outer inch with the egg wash. Spread the mushroom mixture in the center, leaving the 1 inch of egg washed pastry exposed. Place the tenderloin in the center, then roll puff pastry around the meat, flipping it over so the seam is on the bottom. Fold edges in and tuck under, pinching to seal.Brush all exposed pastry with egg wash. Make a few cuts in the top of the pastry for steam to escape. Sprinkle with a pinch of salt. Transfer parchment paper and meat onto a baking sheet. Refrigerate, uncovered, for 30 minutes (or cover and refrigerate up to 6 hours).Bake for 25 to 35 minutes, until puff pastry is golden brown, and meat registers 90°F on an instant-read thermometer. Let rest, uncovered, for 15 to 20 minutes, until thermometer reads 130°F. To easily monitor temperature increase, leave the thermometer in the center of the meat. Transfer to a serving platter, garnish with rosemary sprigs and serve immediately.

Beef Wellington
Serves 4

1 sheet frozen puff pastry

1 center-cut beef tenderloin, about 1 ½ pounds and 7 inches in length
1 ½ teaspoon Dijon mustard
½ teaspoon kosher salt
½ teaspoon ground black pepper

½ medium onion
1 pound mushrooms, washed and trimmed
4 tablespoons unsalted butter
2 garlic cloves, minced
½ teaspoon kosher salt
1 ½ teaspoon dry sherry
1 teaspoon fresh chopped rosemary leaves, plus extra sprigs for garnish

1 egg, beaten
Pinch of kosher salt

Remove puff pastry from the freezer and let thaw on the counter about 30 to 40 minutes, until dough becomes workable.

Meanwhile, lay the tenderloin on a parchment-lined baking sheet. In a small bowl, mix together the Dijon, salt and pepper, then spread all over the meat. Cover with plastic wrap and refrigerate.

In the bowl of a food processor, pulse onion until very finely chopped. Transfer to a bowl. Place mushrooms in the food processor and pulse until very finely chopped. (Alternately, onion and mushrooms can be chopped very finely with a knife.)

In a large nonstick skillet, melt butter over medium-high heat. Add onions and sauté for 3 to 5 minutes, stirring occasionally, until softened. Add mushrooms, garlic, and salt. Turn heat down to medium and cook, stirring occasionally, until all of the liquid from the mushrooms have evaporated and mixture starts to brown, 15 to 20 minutes. Add sherry and stir until evaporated, about 30 seconds. Remove skillet from heat and stir in the rosemary. Let cool for 10 minutes (or refrigerate up to 1 day).

Meanwhile on a piece of parchment paper, roll puff pastry into a 10-inch by 11-inch rectangle. Use a pastry brush to brush the outer inch with the egg wash. Spread the mushroom mixture in the center, leaving the 1 inch of egg washed pastry exposed. Place the tenderloin in the center, then roll puff pastry around the meat, flipping it over so the seam is on the bottom. Fold edges in and tuck under, pinching to seal. Brush all exposed pastry with egg wash. Make a few cuts in the top of the pastry for steam to escape. Sprinkle with a pinch of salt. Transfer parchment paper and meat onto a baking sheet. Refrigerate, uncovered, for 30 minutes (or cover and refrigerate up to 6 hours).

Meanwhile, preheat the oven to 450°F.

Bake for 25 to 35 minutes, until puff pastry is golden brown, and meat registers 90°F on an instant-read thermometer. Let rest, uncovered, for 15 to 20 minutes, until thermometer reads 130°F. To easily monitor temperature increase, leave the thermometer in the center of the meat. Transfer to a serving platter, garnish with rosemary sprigs and serve immediately.