Soak the wild mushrooms in 75ml of just-boiled water for 15 minutes.
To make the butter, mash it with the sage and garlic, shape into a log, wrap in cling film and chill.
Drain the wild mushrooms, adding their soaking liquid to the chicken stock. Wash the rice in a sieve under the tap until the water runs clear.
Put the onion and all the mushrooms into a 30cm sauté pan or shallow casserole dish (the wide base is very important) and sprinkle on the rice (it may not seem much but it expands, don’t worry).
Add the chicken thighs (skin-side up) and pumpkin on top. Drizzle on a little olive oil and season. Bring the stock to the boil and carefully pour it in round the chicken.
Bake for 45 minutes, until the meat is lovely and golden and the stock has been absorbed. Put rounds of the sage butter over the chicken thighs, allow it to melt and serve.