Peel the potatoes and cook in plenty of boiling salted water for about 20 minutes. Peel onion and carrot and dice finely. Clean and wash the leek and cut into rings.
Heat the oil in a pan and fry the onion, carrot and leek. Pluck the goose meat and add to the vegetables. Add sauce from the day before and bring to the boil briefly, season with salt and pepper if necessary.
Place the ragout in an ovenproof dish (20 x 28 cm).
Grate cheese. Heat milk. Drain potatoes and let them evaporate briefly. Pour in the milk, mash everything to puree. Season to taste with salt and nutmeg and fold in cheese. Spread the potato mixture on the ragout and bake in a preheated oven (electric cooker: 175 °C/ circulating air: 150 °C/ gas: see
manufacturer) bake for about 25 minutes. Wash chives, shake dry and cut into fine rolls. Sprinkle the potato topping over the chives.