Roast Fillet of Beef With Mushrooms En Croute

Ingredients

• 1 beef eye fillet (about 1.25kg)
• 2 tbsp olive oil
• 50 gm butter, coarsely chopped
• 300 gm button mushrooms, quartered
• 150 gm cèpes, quartered (see note)
• 3 golden shallots, finely chopped
• 1 small bunch flat-leaf parsley
• 2 slices white sandwich bread, roughly torn
• 300 gm ready-made puff pastry
• 1 egg yolk, for brushing