For the dough, dilute the yeast in a large bowl with 400 ml of warm (37-40 ° C) water. Sift in water, stirring, 1 cup of flour and put in a warm place for 30 minutes.
Separate the yolks from the whites of the eggs. Rub the yolks with sugar until white. Melt and cool the butter a little.
When the dough is suitable, add the yolks with sugar and melted butter, mix thoroughly until smooth.
Slightly warm the milk - up to 36-37 ° C. While stirring so that lumps do not form, sift a little flour into the dough, then add a little milk - you should get a dough of the consistency of thick sour cream. Cover bowl and leave in a warm place for 1 hour.
When the dough has risen, stir it to settle, and put it back in a warm place. Then do it all over again.
Beat egg whites until fluffy and add to the batter, mixing from bottom to top. Let the dough stand for 10-15 minutes, without stirring any more, bake plump pancakes, each time greasing the pan with melted butter.