In a large mixing bowl, combine the whole wheat pastry flour, buckwheat flour, regular whole wheat flour, baking powder, sugar, and sea salt.
Whisk the egg yolks into the milk. Make a well in the center of the dry ingredients and slowly pour in the milk mixture. Stir, pulling the flour from the outside edge in, until just combined. Slowly add the melted butter and continue stirring until combined.
In a medium bowl, beat the egg whites until soft peaks form. Gently fold the egg whites into the batter.
Heat a griddle pan or non-stick skillet. Scoop 1/3 cup of batter into the pan. Cook the pancake until the bottom is golden brown. Flip and cook the remaining side until golden. Repeat until all batter has been used up.