Put the cold water into the paiolo (copper polenta pan), adding a pinch of salt and 250 g of butter and heat. When it boils, gradually pour in first the polenta flour and then the buckwheat flour. Stir constantly, making sure the polenta is thoroughly mixed to give a smooth, thick consistency. As it cooks, add the remaining butter a piece at a time and just before it is ready, two handfuls of breadcrumbs.
A few minutes before pouring the polenta out onto the basla or wooden serving board, add the cheese.
Tip the polenta out and serve before the cheese has time to melt completely.