Place the flour and salt into a bowl and crumble in the fresh yeast. Place the milk into a pan over a low heat and gently warm through. Pour the warm milk into the flour, mixing thoroughly with a whisk to form a thick batter. Put aside for an hour. When the batter is ready, it will have foamed up. Quickly whisk the egg whites to soft peaks and fold into the batter mixture along with the chopped chives. Heat a large pan with a little olive oil and drop in spoonfuls of the batter. Cook for 45-60 seconds until golden brown underneath, then turn over and cook for 30 seconds on the other side. Remove the blini from the pan and place onto kitchen paper. Repeat this process with the remaining batter. To serve, place a spoonful of sour cream onto each blini, top with the smoked salmon and a side serving of caviar in a small bowl on the side