Put buckwheat flour, wheat flour, crushed flaky salt, and baking powder in a large bowl.
Mix well and add the yogurt.
Whisk well until the batter is smooth.
Add the water and whisk again.
Separate the eggs into whites and yolks.
Put the egg whites in a clean, medium-sized bowl and set aside.
Whisk the egg yolks into the smooth batter.
Melt the butter and whisk it into the batter until it is completely smooth in consistency.
Let the batter rest on the kitchen counter for about ½ hour.
Whisk the egg whites stiff with a hand mixer and gently fold them into the batter using a spatula.
Put a pinch of butter in the holes of a mini blini pan.
It is also quite possible to place small, fine dollops of the batter directly on a hot, regular pan.
Optionally, use a large disposable piping bag with a relatively small hole so you can easily control the quantity that comes out.
Gently stir the batter occasionally.
Bake the blinis briefly on high heat until they are lightly golden on both sides.
Let them cool and wrap them until ready to serve.