First Step: SEAR THE BEEF

1. Trim and Cut the Beef: Start by trimming the beef tenderloin of any excess fat and silver skin. Then, cut it into small, 1-inch cubes.
2. Sear the Beef: Heat 2 tablespoons of olive oil in a large skillet over medium-high heat. Once the oil is hot, season the beef cubes with salt and pepper, then add them to the skillet. Sear the beef on all sides for about 2-3 minutes per side, ensuring a nice golden crust.
3. Coat with Mustard: Remove the beef from the skillet and let it cool slightly. Brush each cube with Dijon mustard. This will help the mushroom mixture adhere and add extra flavor to the beef.
4. Chill the Beef: Once the beef is coated with mustard, wrap the cubes tightly in plastic wrap and place them in the fridge to chill for about 30 minutes. This step helps the beef hold its shape when wrapped in puff pastry.

Second Step: MAKE THE MUSHROOM DUXELLES

1. Cook the Mushrooms: In the same skillet used for searing the beef, melt 2 tablespoons of butter over medium heat. Add the chopped mushrooms, shallots, and garlic. Cook, stirring occasionally, until the mushrooms have released their moisture and the mixture is dry, about 8-10 minutes.
2. Add the Wine and Thyme: Once the mushroom mixture is dry, add the white wine and thyme. Continue to cook until the liquid has evaporated, and the mushrooms have absorbed the wine, leaving a rich and concentrated flavor. Season with salt and pepper to taste. Set the mixture aside to cool.

Third Step: ASSEMBLE THE MINI BEEF WELLINGTON BITES

1. Prepare the Puff Pastry: Roll out the puff pastry sheet on a lightly floured surface. Cut the pastry into squares large enough to wrap around the beef cubes (about 3×3 inches).
2. Add the Duxelles: Spoon a small amount of the mushroom duxelles into the center of each pastry square. The duxelles will form the base for the beef.
3. Wrap the Beef: Place a chilled beef cube on top of the duxelles. Carefully fold the corners of the pastry over the beef, sealing the edges to encase the beef and mushrooms. Make sure the pastry is tightly sealed to prevent leaks during baking.
4. Egg Wash: Brush the top of each puff pastry package with a beaten egg to give it a golden, glossy finish once baked.

Fourth Step: BAKE THE MINI BEEF WELLINGTONS

1. Preheat the Oven: Preheat your oven to 400°F (200°C). Line a baking sheet with parchment paper or a silicone baking mat.
2. Bake the Wellington Bites: Place the assembled mini Beef Wellington bites on the prepared baking sheet. Bake in the preheated oven for about 20-25 minutes, or until the puff pastry is golden brown and crisp. The beef inside should be cooked to your desired level (medium-rare is ideal for these bites).
3. Cool Slightly: Once baked, remove the mini Beef Wellington bites from the oven and let them cool for a few minutes before serving.

Final Step: GARNISH AND SERVE

1. Garnish: For an extra touch of elegance, garnish the mini Beef Wellington bites with small sprigs of fresh thyme.
2. Serve: Arrange the mini Beef Wellington bites on a platter and serve immediately while they’re warm. These little bites make for a stunning appetizer or party snack.