Sift the flours with a good pinch of salt into a bowl. Add the yeast and the warm milk and beat with a balloon whisk until smooth. Stir the egg yolks into the batter. Cover with a tea towel and leave to rest for 1 hour, in a warm place away from draughts, until risen.
When ready to cook, add a pinch of salt to the egg whites and whisk until they form slightly soft peaks. Stir the batter, then gently fold in the beaten egg whites.
Heat a heavy-based frying pan over a moderate heat. Grease sparingly with butter, then pour in a small ladleful of the blini mixture and spread out until it is about 12 cm in diameter. Cook for 1½ minutes on each side.
Place the cooked blini on a heated plate, cover and keep warm while you make the rest. Make seven more blini in the same way, using the rest of the mixture. Serve warm topped with sour cream and smoked salmon.
• Covered in plastic wrap, blini keep very well in the fridge. Reheat them in a low oven, wrapped in foil. You could also reheat them in a frying pan over a low heat, taking care not to overheat. • If you are entertaining, splash out and serve the blini with crème fraîche and roe.