Bring 1 litre of water, butter and 1 teaspoon of salt to the boil in a saucepan. Pull the pot from the stove, stir in polenta. Simmer polenta with a wooden spoon at low heat for about 15 minutes, stirring frequently and vigorously. Grate parmesan. Stir 50 g parmesan into the polenta, season with salt and nutmeg. Put the polenta on a greased baking tray and flatten or smooth it down to a thickness of about 0.5 cm. Put polenta in a cool place for about 2 hours.
Peel and halve the onion and cut into thin rings. Heat the oil in a pot. Sauté the onion for 2-3 minutes, then add Bolognese sauce and cream. Let the sauce simmer for about 2 minutes and season to taste with salt and pepper if necessary
Cut out 18 circles (each approx. 8 cm Ø) from the polenta. Place 6 circles on the bottom of 6 greased ovenproof trays (approx. 8 cm Ø, approx. 150 ml). Cover with half of the Bolognese sauce and sprinkle 1/3 of the Parmesan cheese on top. Place one polenta slice on each and sprinkle with 1/3 of the cheese. Finish with polenta and parmesan. Bake in a preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: see manufacturer) for 20-30 minutes. Serve immediately
waiting time approx. 1 3/4 hours