Place the plain and buckwheat flours, salt and yeast in a bowl and stir to combine.
Place the milk and sour cream in a saucepan over low heat and cook, stirring, for 2 minutes or until lukewarm. Add the eggyolk and whisk to combine. Gradually add the milk mixture to the flour mixture, stirring until smooth. Cover with a clean, damp cloth and set aside in a warm place for 30 minutes or until bubbles appear on the surface.
Whisk the eggwhite until soft peaks form, add the mixture and stir well to combine.
Heat a lightly greased, large non-stick frying pan over medium heat.
Cook teaspoonfuls of the mixture for 1-2 minutes or untill bubbles appear on the surface. Flip and cook for 1-2 minutes or untill golden. Allow to cool. Makes 30.