In a medium bowl mix buckwheat flour, yeast and salt.
Add warm milk and stir. Cover and set in warm place to rise for 1 hour. (Can be prepared to this point and kept in the fridge over night. Bring to room temperature to continue.)
Stir in the butter, egg yolk and buttermilk.
Whisk egg white to soft peaks and gently fold into batter. Cover and let sit 30 minutes.
Heat a large skillet or pancake griddle over medium heat.
Brush with melted butter. Pour 2-3 tablespoon batter onto griddle or pan depending on the size of pancake you want.
Cook until bubbles form on the surface, about 1 minute. Flip pancakes and cook a little less on the second side.
Remove from pan and keep warm while cooking them all.
Serve warm with lox, (gravlax or smoked salmon), sour cream (or crème fraîche), fresh dill and lemon.