Peel and wash the potatoes and cook in salted water for about 20 minutes. Then drain and press through a potato press. In the meantime, crumble the yeast and dissolve in 100 ml of lukewarm water with sugar.
Put the corn starch, buckwheat flour and rice flour in a bowl and press a depression in the middle. Add the yeast mixture and cover lightly with flour. Cover and leave to rise in a warm place for about 5 minutes.
Add milk, potatoes, salt (ground caraway and coriander to taste) and binding agent and knead to a smooth dough. Cover and leave to rise for 20-30 minutes. Then knead again and leave to rise for 20-30 minutes.
Knead the dough, form into a loaf, place on a baking tray lined with baking paper and leave to rise for 20-30 minutes. Bake in a preheated oven (electric: 175 °C/ gas: level 2) for approx. 45 minutes.
Let the bread cool down. Results in about 20 slices. Serve with butter, Gruyère cheese and grapes.