Mary Berry's beef Wellington recipe

Ingredients

• 1.5 kg beef fillet, trimmed and tied
• 2 tbsp sunflower oil
• 45 g butter
• 1 small onion, chopped
• 250 g flat mushrooms, finely chopped
• 175 g smooth liver pâté
• 400 g ready-made puff pastry
• 1 egg, beaten
• 1 pinch salt and black pepper