Steps
- Freeze 200g of unsalted butter until solid. Mix 400g of all-purpose flour, 1 tablespoon of thyme leaves, and ½ teaspoon of salt; grate in the butter.
- Beat 2 eggs and reserve half, covered in the fridge. Mix the rest into the flour with 130ml of cold whole milk; knead for 1 minute, wrap, and chill for 1 hour.
- Cover 25g of dried mixed mushrooms with 150ml of boiling water until softened, then drain.
- Cut half of 750g of cremini mushrooms and 500g of portobello mushrooms into ¾in / 2cm pieces; halve the rest. Add 200g of button mushrooms.
- Heat 3 tablespoons of olive oil in a pan over high heat; brown the fresh mushrooms in two batches for 10 minutes each, adding oil if needed. Remove.
- Melt 50g of butter over low heat. Soften 1 sliced onion with a pinch of salt for 10-15 minutes. Stir in 50g of all-purpose flour for 2 minutes, then 1 teaspoon of white wine vinegar and 3 tablespoons of brandy for 1-2 minutes.
- Gradually stir in 500ml of vegetable stock, 1 teaspoon of Marmite, 150ml of heavy cream, and ¼ teaspoon of black pepper. Simmer, add all the mushrooms, season with salt, and cool completely. Stir in ½ small bunch of finely chopped tarragon.
- Transfer to an 11in / 28cm pie dish. Roll the dough to ½in / 1cm thick; cut strips to cover the damp dish rim. Reroll the rest as a lid, seal, crimp, and cut a vent.
- Mix the reserved egg with a splash of milk; brush the lid and chill for 30 minutes. Preheat the oven to 400°F / 200°C. Brush again, bake for 40-45 minutes, until golden, and rest for 15 minutes.