Cut the spinach and sauté it in a little oil until the water evaporates. Boil potatoes and grate them on a grater. In a bowl, mix the spinach and potatoes, chopped onions, feta cheese, grated cheese, yoghurt with baking soda dissolved in it, 4 tablespoons of breadcrumbs and salt to taste.
Mix everything well and leave for 15 minutes in the refrigerator. Heat the oil and fry the patties, formed from the mixture using a spoon. Fry on both sides with a spatula and drain on paper towels.
Serve with vegetables and a sauce of your choice.