Blini with Red Caviar and Sour Cream

1 pkt active dry yeast
1/2 cup warm water
1 cup milk
1 1/2 cup flour
3 lrg egg yolks
1/2 tsp salt
1 pch sugar
6 tbsp unsalted butter, melted
3 egg whites
1/2 pt sour cream
3 1/2 oz jar red caviar

Proof yeast in warm water for 5 minutes. Put the yeast mixture, milk, flour, egg yolks, salt, sugar, and melted butter in a blender or food processor. Blend at high speed for 40 seconds. Turn machine off, scrape down, and blend another few seconds.
Pour batter into a bowl that is large enough to accommodate the rising. Cover loosely, and set in a warm place to rise for 1 1/2 to 2 hours. Do not let the batter rise much longer or blini will taste overfermented.
Beat egg whites until stiff. Fold into batter. Heat a heavy skillet or griddle. Brush with butter. Drop blini batter by teaspoonfuls into hot pan. Turn when first side is lightly browned, and cook briefly on second side. Keep pancakes on a heated platter until all the batter is used.
Arrange warm blini on a tray lined with a starched linen napkin. Put a small dollop of sour cream in the center of each, then a few grains of caviar. A strip of smoked salmon decorated with a sprig of dill may be substituted for the caviar, if desired.
Blinis may be cooled, wrapped in foil, and refrigerated for use the next day. Warm in 300 degree oven before serving.