Directions: In a medium size sauce pan add potatoes, cover with water and bring to boil. Reduce heat and cook for 20 minutes, then drain, mash and set aside. (For the better taste, always try to boil potatoes unpeeled, maintain their nutritional value as well.)
Preheat the oven to 220 degrees C.
In a mixing bowl beat eggs, add the cream and salt, and whisk well all together. Add mashed potatoes and whisk until well blended. Add cheese, finely chopped onion, ( may be sauted, improves taste), mix well, then stir in the baking powder.
Brush with oil or butter a square casserole, heat it in the oven, pour the potato mixture and level. Bake for 35 minutes, or until top is golden - brown. Cool for 5 minutes before cutting.
In a a small saucepan melt 1/2 cup butter. Cut the kartoshnik into 3 inches squares. Before serving, sprinkle with melted butter, add a dollop of sour cream or yogurt and green onions.