In a large mixing bowl, whisk together the buckwheat flour, all-purpose flour, instant yeast, sugar, and salt.

Pour in the warm milk and melted butter. Whisk until the batter is smooth.

Add the egg yolk to the batter and whisk to combine. Cover the bowl with a clean towel and let it rest in a warm place for about 30 minutes until bubbly.

In a separate small bowl, beat the egg white until soft peaks form, then gently fold it into the rested batter to create a light texture.

Heat a non-stick skillet over medium heat and lightly grease with a little extra butter or oil.

Drop tablespoon-sized portions of batter into the pan. Cook for about 1-2 minutes until bubbles appear on the surface, then flip and cook for another minute until golden brown.

Transfer cooked blini to a plate. Repeat with remaining batter.

To serve, top each warm blini with a dollop of sour cream, a slice of smoked salmon, and a sprig of fresh dill.