Mini Beef Wellington

Bahan-bahan (6 porsi)

• 1 tbsp butter
• 1 lb mushrooms (finely chopped)
• 2 -3 sprigs fresh thyme
• 1 lb beef tenderloin (or filet, 1.5" cubed)
• 1 tbsp neutral oil
• salt and freshly ground pepper
• 1 -2 tbsp dijon mustard (or to taste, Grey Poupon preferred)
• 6 slices Prosciutto di Parma
• 2 sheets puff pastry (thawed)
• 1 egg yolk (lightly beaten with 1 tsp water)