Mix together the buckwheat flour, white flour, baking powder and salt with 3/4 cup/175 ml cold water to make a paste. Add the boiling water and mix until smooth and runny. Let the batter sit for 30 minutes.
Heat a cast-iron griddle. Without adding any fat, ladle the mixture onto the griddle and let it run into small pancakes. Watch bubbles form all over the cakes and wait until the top of the cakes are completely dry. (Do not flip the ployes until they are completely cooked.) Once they look dry, flip them and just "kiss" the pan with the other side.
Keep the cooked ployes warm in a warm oven while you fry the rest.