Combine the egg, kefir, flour, salt, sugar and soda slaked with vinegar. Stir with a whisk.
Finely chop the onion and add to the dough, mix and let stand for 5 minutes.
Grease the pan with vegetable oil, put the dough with a spoon and fry for about 2 minutes on each side.
Serve the finished pancakes with sour cream or with your favorite sauce.