These are the pancakes one eats in the last week before Lent proper, maslenica, Cheesefare Week. No cheese here, though, just fish and lots of butter.
Dissolve the yeast in a bit of the milk, heated to lukewarm, with the sugar. Sift both kinds of flour together with the salt. Put about two-thirds in a mixing bowl, make a well in the centre, pour in the yeast solution and about two-thirds of the milk (also lukewarm), and stir to make a thick batter. Cover with a cloth and let it rise in a warm place for 2-3 hours.
Warm up the rest of the milk. Add some of it to the batter, stir well and let it rise for 5 minutes. Then add the egg yolks, the rest of the flour and the rest of the milk and let the batter rise for another 20 minutes, while you beat the egg whites to soft peaks. Fold the egg whites into the batter and immediately make the bliny.
It's most convenient to fry several at a time in a large flat frying pan. They should be about 3-4 inches across (the size of the palm of your hand if you're medium-sized).
Eat bliny with different kinds of smoked fish, real or fake caviar, prawns, etcetera. Serve melted butter and sour cream on the side.