Sift buckwheat flour and plain flour into a bowl and mix with salt.
Whisk eggs and one egg white into the center of the flour to create a paste.
Combine yeast, sugar, and milk in a separate bowl and let stand.
Whisk the yeast mixture into the flour mixture to form a smooth batter.
Stir in the melted butter.
Cover and leave in a warm place for one hour.
Whisk the second egg white until light and fold it into the batter.
Heat oil in a pan and pour batter to make 10cm diameter blinis.
Turn the blinis when bubbles appear and cook the other side.
Keep cooked blinis warm while finishing the batter.
Slice the roasted peppers into thin strips.
Mix sour cream, horseradish, tarragon, and lemon juice in a bowl.
Top each blini with one tablespoon of cream and pepper strips.
Garnish with an olive and black pepper.