Air Fryer Beef Wellington

For the Beef Wellington

• 1 beef fillet steak (6–8 oz, about 1.5 inches thick)
• 1 tablespoon olive oil
• Salt and black pepper, to taste
• 2 teaspoons Dijon mustard
• 4 oz mushrooms (finely chopped)
• 1 teaspoon butter
• 1 clove garlic, minced
• 1 teaspoon fresh thyme
• 2 slices prosciutto
• 1 sheet puff pastry (thawed if frozen)
• 1 egg yolk, beaten (for egg wash)