Sprinkle steaks with 1/2 teaspoon salt and 1/4 teaspoon pepper. In a large skillet, brown steaks in 1 tablespoon oil for 2-3 minutes on each side. Remove from skillet and refrigerate until chilled.
In the same skillet, saute mushrooms and onion in remaining oil until tender. Stir in remaining salt and pepper; cool to room temperature.
Preheat oven to 425°. On a lightly floured surface, roll each puff pastry sheet into a 14x9-1/2-in. rectangle. Cut into two 7-in. squares (use scraps to make decorative cutouts if desired). Place a steak in the center of each square; top with mushroom mixture. Lightly brush pastry edges with water. Bring opposite corners of pastry over steak; pinch seams to seal tightly.
Place in a greased 15x10x1-in. baking pan. Cut 4 small slits in top of pastry. Arrange cutouts over top if desired. Brush with egg.
Bake 25-30 minutes or until pastry is golden brown and meat reaches desired doneness (for medium-rare, a thermometer should read 135°; medium, 140°; medium-well, 145°).
Beef Wellington Tips
What cut of beef is best for beef Wellington?
Beef tenderloin is the cut of beef that’s most commonly used for beef Wellington recipes. It cooks for a similar amount of time as the puff pastry it's wrapped in, which ensures you won't wind up with overcooked beef.
What do you serve with beef Wellington?
Your go-to side dishes for steak will likely work well as beef Wellington sides. Try serving this beef Wellington recipe with one of our favorite mashed potato recipes, or these Garlic Roasted Brussels Sprouts.
Can you prep beef Wellington the night before?
Yes, beef Wellington can be prepped ahead of time—just be sure it’s wrapped properly and refrigerated until baking. If you're using homemade puff pastry, make it ahead of time and portion appropriately. As a shortcut, store-bought puff pastry works just as well and is a great time saver!