1-First Step: Prepare the mise en place. Cube the 1.5 lbs beef tenderloin into 1-inch pieces and season with salt and pepper. Finely chop or pulse 8 oz mushrooms, 1 shallot, 2 garlic cloves, and 1 tbsp thyme in a food processor for duxelles. Thaw 1 puff pastry sheet and slice 4 oz prosciutto into thin strips. This setup keeps things organized for smooth assembly, adaptable for smaller batches if needed.

2-Second Step: Sear the beef. Heat 1 tbsp olive oil in a skillet over high heat. Sear beef cubes 1 minute per side until browned but rare inside. Work in batches to avoid crowding. Cool on a plate; optional brush with Dijon mustard for extra tang. This quick sear locks in juices, key for pink centers in your mini beef wellington bites. Vegetarians can skip beef here.

3-Third Step: Cook the duxelles. In the same skillet, add remaining 1 tbsp oil over medium heat. Sauté mushroom mixture 10 minutes, stirring until moisture evaporates and it forms a thick paste. Season with salt and pepper. Spread on a plate to cool fully. Drying prevents soggy pastry, a common fix for perfect puff pastry bites.

4-Fourth Step: Assemble the wraps. Lay prosciutto slices overlapping on plastic wrap in a 6×4-inch rectangle. Spread cooled duxelles evenly, leaving a border. Place 1 seared beef cube in center, wrap prosciutto tightly around like a log using the plastic. Repeat for all cubes. Chill or freeze 15 minutes to firm up. This pro wrap holds shape during baking.

5-Fifth Step: Cut and wrap in pastry. Roll thawed puff pastry to 1/8-inch thick; cut into 3×3-inch squares (about 24). Place 1 beef log seam-side down in center of each square. Fold corners over top, pressing to seal. Brush with beaten egg wash for shine. Arrange on parchment-lined baking sheets, seam down. For dietary tweaks, use vegan pastry here.

6-Final Step: Bake and serve. Preheat oven to 425°F. Bake 18-22 minutes until pastry is deep golden and puffed. Internal beef temp: 135°F for medium-rare (carryover adds 5°F). Rest 5 minutes. Serve with mustard aioli or horseradish. These mini wellingtons shine as appetizers; pair with a refreshing drink for parties. Yields 24; serves 8-12 as starters.