These traditional Russian pancakes are best with authentic garnishes: a dab of creme fraiche and a spoonful of caviar.
Sprinkle yeast over water. Let stand until foamy, about 5 minutes. Stir together flour and 1/2 teaspoon plus a pinch of salt. Stir together buttermilk, butter, sugar, and egg yolks in a large bowl; whisk in yeast mixture, then flour mixture. Let stand, covered, in a warm place for 30 minutes.
Beat egg whites until stiff peaks form; fold into batter. Let stand for 10 minutes.
Heat a medium nonstick skillet over medium heat, and coat with a thin layer of butter. Add a scant tablespoon batter for each blin (about 6 or 7 per skillet), and cook, flipping after bubbles appear at edges and color turns golden, 1 1/2 to 2 minutes per side. Transfer to a parchment-lined tray, andlet cool for 30 minutes. Garnish with creme fraiche and caviar.