Mix the two flours with the dry yeast and dry leaven. Mix the sugar, salt, herbs and nutritional yeast. Peel the potatoes, grate finely and add to the flour. Knead with an electric mixer, adding the broth until it forms a smooth, firm dough. Cover the dough and let it rest in a warm place for about 30 minutes.
Knead the dough briefly on a floured surface by hand. Form into a loaf. PLace on a greased baking sheet and let rise for another 30 minutes. Preheat the oven to 200°C (approximately 400°F). Brush the bread with water and bake in a preheated oven for about 50 minutes until golden brown.