Sift the flour into a bowl make a hole and pour soaked in warm water yeast. Let it stand for 30 minutes. Add grated potatoes, melted butter and salt to taste, Knead an elastic dough. Divide into pieces and roll out, place flatbreads into a baking sheet, grease with the butter and sour cream, sprinkle with cumin and bake at 225 degrees Celsius for 20 minutes. Serve hot.