Dissolve the yeast in the milk. Incorporate the buckwheat flour and mix to form a smooth paste. Cover and set aside in a warm place for 1 hour to rise.
Add the bread flour, buttermilk, beer, and egg yolks, stirring until smooth. Cover and set aside in a warm place for 1 hour to rise again. After the second rising, the blini batter may be reserved in the refrige