01 -
Generously season beef tenderloin pieces with salt and black pepper.
02 -
Heat olive oil in a skillet over high heat. Brown half of the beef pieces for 1-2 minutes on each side, then remove.
03 -
Preheat oven to 400°F (200°C).
04 -
In the same skillet, sauté minced onion and sliced mushrooms over medium-low heat for 10 minutes until softened.
05 -
Transfer the sautéed mixture to a food processor. Add black olives and blend until combined.
06 -
Unfold puff pastry and cut into 3-3.5 inch squares. Spread mustard on each square, add a spoonful of mushroom filling, then top with a browned beef piece.
07 -
Place assembled bites on a parchment-lined baking tray. Brush tops with beaten egg. Bake for 10-15 minutes until pastry is puffed and golden brown.