Elegant Beef Bites with Mushrooms and Pastry

Ingredients

• 12 oz beef tenderloin, trimmed
• 1 tbsp olive oil
• Salt and freshly ground black pepper, to taste
• 9 oz cremini or button mushrooms, finely chopped
• 2 tbsp unsalted butter
• 1 small shallot, finely diced
• 1 garlic clove, minced
• 1 tbsp fresh thyme leaves, chopped
• 1 tbsp dry sherry or white wine
• 1 sheet (9 oz) puff pastry, thawed if frozen
• 6 thin slices prosciutto
• 1 egg, beaten (for egg wash)