Choose a new cookbook worth up to £28 when you subscribe to our magazine.
Heat oven to 200C/180C fan/gas 6. Unroll the pastry and cut into 4 rectangles. Use a sharp knife to score a 1cm border around each, place on a baking tray, then chill until needed.
Heat the butter and oil in a large frying pan, add the mushrooms and cook over a high heat, stirring, for about 10 mins, or until golden brown and almost all the liquid has evaporated. Season, add the garlic and walnuts, and cook for 1 min. Set aside.
Put the goat’s cheese in a bowl, season and stir through the thyme leaves. Remove the pastry from the fridge and spread the cheese over the centres. Top with the mushroom mixture, then brush the edge of the pastry with beaten egg for a glossier finish, and bake for 20-25 mins or until the pastry is golden and crisp. Top with the remaining thyme sprigs and a good grinding of black pepper. Serve with a baby leaf salad.