Mushroom Wellington with Tarragon Smashed Peas

Ingredients

• 50g butter
• 2 tbsp olive oil
• 2 leeks, finely sliced
• 1 tbsp fresh thyme
• 2 cloves garlic, crushed
• 600g mushrooms, brown or Portobello
• 300g spinach leaves, wilted and chopped
• 200g soft goats’ cheese, crumbled
• 500g block puff pastry
• 1 egg yolk
• 2 tbsp milk
• 30g butter
• 400g frozen peas, thawed
• 2 tablespoons chopped fresh tarragon
• 1 tablespoon lemon juice