In a small bowl, stir together the yeast, warm water, sugar and first measure of flour. Cover and set aside until doubled, about one hour.
Beat in all the rest of the ingredients, except for the egg whites, using the lesser amount of flour. Once incorporated, whisk until smooth and then cover. Set aside to rise until doubled in bulk, about 1½ hours.
Stir the batter well again, recover, and let rise once more for about 45 minutes.
Whisk the whites to soft peaks and fold into the batter. Don’t whip the egg whites before you are ready for them, as they won’t hold. Let the batter rest for another ten minutes.
Heat a well-seasoned 8 inch cast iron skillet or heavy-bottomed nonstick skillet over medium heat.
Rub the pan with peanut oil. Ladle in about ¼ cup of batter, tilting and swirling the pan to completely cover the bottom of the pan with a thin layer of batter. Cook until the top of the blin is bubbly and the bottom is golden brown.
Carefully turn and cook the other side for about 30 seconds, brushing some melted butter on the cooked side.
Repeat with another ¼ cup of batter. Taste this one (the first is generally for the cook) and check to see if it needs more salt or sugar. If the pancake breaks when you try to fold it, whisk the reserved ¼ cup of flour into the batter. If the pancake is too thick, whisk in a little more warm milk.
Continue making blini until you have used all the batter. Serve hot or warm with crème fraiche and caviar.
To make crème fraiche, whisk 2 tablespoons of buttermilk into 1 cup of heavy cream. If you can find it, use pasteurized, not ultra-pasteurized cream.
Let the mixture sit out at room temperature until nicely thickened. This could take up to 36 hours, but check it every 12 hours.
Once thickened, refrigerate until cold.