Wash the thyme, shake dry and, except for something to garnish, pluck leaves from the stalks. Peel and clean the carrot. Peel onion. Chop carrot and onion roughly. Wash guinea fowl and season inside with salt, pepper and thyme, outside with salt and pepper only.
Place on the fat pan of the oven. Arrange the vegetables around it. Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for approx. 1 hour. In the meantime, peel the potatoes and cook in boiling salted water for about 20 minutes.
Peel and quarter apples, remove core. Roughly dice quarters. After 15 minutes cooking time add apples to the potatoes. Bring milk, 50 g butter and 100 g chestnuts to the boil. Season with salt and pepper.
Finely puree with a blender. Drain the potato water. Add the mashed chestnuts to the potatoes and mash them with a potato masher into puree. Coarsely chop 50 g chestnuts. Heat 1 tablespoon of butter and roast the chopped chestnuts for about 3 minutes.
Remove guinea fowl from the oven, divide into portions and keep warm. Dissolve the roast with 150 ml water, pour it through a sieve into a pot. Stir starch and 2 tablespoons of water until smooth. Bring the roast stock to the boil and thicken with starch.
Arrange puree, meat and sauce on plates. Sprinkle with roasted chestnuts. Garnish with thyme.