In a medium saucepan, heat the butter over medium heat. Add the onion and mushrooms and cook until softened, about 5 minutes.
Add the ground beef and cook until browned, about 7 minutes. Add the garlic powder, nutmeg, thyme, and salt and pepper to taste. Cook for an additional 2 minutes.
Add the red wine and cook for 2 minutes, stirring frequently. Add the flour and beef broth and cook until the sauce is thickened, about 3 minutes.
Remove the sauce from the heat and set aside.
Unfold the puff pastry sheets and cut into 4-inch squares. Place a spoonful of the beef mixture in the center of each square and fold the edges up to form the wellingtons. Place on a baking sheet lined with parchment paper.
Brush the tops of the wellingtons with the beaten egg and bake for 15 minutes, or until golden brown.
Serve with the red wine sauce.
Interesting Facts
Beef Wellington is a classic British dish that has been around since the 19th century.
The dish is said to have been named after the Duke of Wellington who was a British military leader.
Beef Wellington is made with a combination of beef, mushrooms, onions, garlic, and seasonings wrapped in puff pastry.