1. In a large bowl, mash cheese with a fork. Add egg and mix well. Stir in sugar and salt. 

2. Add flour, a little at a time, until dough is firm enough to knead by hand. Continue adding flour and kneading until dough can be shaped easily with hands. 

3. Dust hands with flour and scoop up a piece of dough about the size of a medium apple. Roll into a ball between palms and press to form a pancake about 1 inch thick. Make a batch of 3 or 4 before frying. 

4. Pour a thin layer of oil into a large frying pan and heat over medium heat for 1 minute. Carefully place pancakes in pan with a spatula and fry for 3 to 4 minutes, or until bottoms are golden brown. Turn over and fry until second side turns golden brown. Remove and place on paper towels. 

5. Continue making and frying sirniki, adding more oil to pan when necessary, until dough is finished. Sprinkle with sugar and serve with a scoop of sour cream