Yield 6 servings
Dissolve the yeast in ¼ cup of the milk, heated to lukewarm. Then stir in the sugar and 1¼ cups more of the milk. Add the buckwheat flour and stir briskly to mix. There should not be any lumps. Cover the sponge mixture and let rise in a warm place for 1 hour.
Melt the butter and mix it with the egg yolks and the sour cream. Add this mixture to the sponge, along with the remaining ½ cup of milk, the salt, and the all-purpose flour. Cover the bowl and let rise in a warm place for 2 hours. (Make sure you have beaten the flour in well; there should not be any lumps.)
Beat the cream until stiff. Beat the egg whites until stiff but not dry and fold them into the cream. Fold this mixture into the batter. Then let the batter rest for 30 minutes more (if the batter seems too thick at this point, a little warmed milk may be carefully added).
Heat one or several cast-iron pans. Brush with butter (and a little vegetable oil, if desired); when the butter is hot, the pans are ready.
Use 2 tablespoons of the batter for each blin, taking it from the top of the batter each time so that the rest doesn’t fall. Pour it onto the prepared pan and swirl the pan to make a pancake about 5 inches in diameter.
Cook the blin for just a few minutes, until bubbles appear on the surface, then turn and cook the other side until faintly browned. The blini are best served hot from the pan, but if they must be held, pile them in a deep dish, brushing each one with butter, and cover the top of the dish with a linen towel.
Recipe by Darra Goldstein at https://darragoldstein.com/russian-pancakes-blini/