Tender beef Wellington with steamed vegetables recipe

Ingredients

• 1 large_piece 800g piece beef fillet
• 1 tablespoon olive oil
• 25 gram butter
• 1 small brown onion (80g), chopped finely
• 125 gram button mushrooms, chopped finely
• 150 gram chicken or duck liver pate
• 2 sheets puff pastry
• 1 egg, beaten lightly