In a mixing bowl, dissolve yeast in the lukewarm water.
Add milk and 3/4 cups of the pancake mix.
Mix until smooth.
Cover with a towel and set aside in a warm place to rise for 2 hours.
Add baking soda to buttermilk.
Beat egg yolks well.
Add melted butter, buttermilk mixture, and remaining pancake mix.
Mix well.
Add this to the raised mixture and stir well.
Add the salt to the egg whites and beat until stiff but not dry.
Fold beaten egg whites into the batter.
For each pancake, drop 2 Tbsp. batter onto a well-greased griddle.
Cuck until browned on both sides, but turn only once.
Serve blini warm topped with cottage cheese and caviar.