Sift the buckwheat flour, white flour and salt into a large bowl, then make a well in the center. Add half the ilk and stir in the flour to make a thick, smooth paste like batter. Beat until well blended, then gradually beat in the remaining milk. Cover the bowl with plastic wrap and set aside for 15-45 minutes.
Uncover the batter and beat in 5 fl oz/150ml of the water, then slowly beat in more water until the batter is the consistency of light cream. Add half the clarified butter and beat until well blended and not visible on the surface.
Heat a 9-inch crepe pan or skillet over medium high heat until it is very hot.
Spoon the oil into the pan and spread it over the surface. Reduce the heat to medium and continue heating the pan until a few drops of better set on contact.
Rub the surface of the pan with clarified butter. Drop a small ladleful of batter in the center of the pan and immediately lift and tip the pan so the batter covers the bottom as thinly as possible. Cook the crepe until is is golden brown and set on the bottom with holes starting to appear on the surface, then flip it over, using a metal palette knife., and cook until the other side is set.
Transfer the crepe to a plate and keep warm. Repeat until all the batter is used.
Thinly slice the goat cheese. Arrange the crepes on the counter in front of you, then divide the goat cheese and bell peppers among them. Turn the sides of each crepe into the center, then fold in at the ends to make a square packet.
Reheat the pan. Rub with clarified butter, add the crepes, folded side down, and cook for 90 seconds, then flip over and cook for an additional 30 seconds, or until the crepes are hot and the filling is warmed through. Serve hot, garnished with cherry tomatoes.