ok, posting this again here so I can find it
This traditional butter cake of the Breton region, almost a shortbread, is based on one of the staple grains of Brittany, buckwheat (called blé noir in French, or sometimes farine de sarrasin). Buckwheat frequently turns up as a major grain in places where there is little arable land to spare (mountainous regions usually) or places where the climate is too cool or wet to grow good wheat. It's a dense grain, lacking gluten, and so will never raise very high when used for baking: which is possibly why a much better-known baked product of Brittany is the famous but extremely flat Breton crépe, the galette.
The Gateau breton, however, is worth making for a chance to experience the intense nutty flavor of buckwheat. There are a number of recipes for gateau breton out there that include no buckwheat at all... which may make the cake easier to deal with or more mainstream in flavor, but which nonetheless miss the point of tasting the ingredients that make this cake a specialty sought after by people all over France.
Click on "read more" for the recipe...
For gateau breton, you need:
300 g buckwheat flour
150 g granulated sugar
4 egg yolks
125 grams lightly salted butter
1 tsp baking powder
Optional: zest of an orange (preferably a bitter or Seville orange)
In a bowl, sift the sugar, buckwheat flour and baking powder together: mix well. Separate the eggs into whites and yolks and freeze the whites to use for something else: put aside one egg yolk to brush the cake with before baking.
Make a well in the flour/sugar mixture. Add the egg yolks and mix very well with a wooden spoon. Then rub the dough through the fingers until crumbly. Using a pair of knives or a pastry blender, cut the butter into the dough until evenly distributed.
Butter a springform baking pan / tin and pat the dough into it. Brush the top of the cake with the remaining egg yolk: then, with a fork, score the top of the cake crosswise several times in each direction to create a diamond / lozenge pattern.
Bake in a moderate oven (180 degrees C, 360 degrees F) for about forty-five minutes. Allow the cake to stand and cool in the tin for ten minutes or so before turning out.