Gateau Breton au blé noir (Buckwheat Cake) - Untested

 https://www.lesfoodies.com/felicia/recette/gateau-breton-au-ble-noir

For the cake:

140 g black wheat flour (buckwheat)

140 g of ordinary flour

1/2 tsp. salt 

1/4 tsp. cinnamon

240 g of butter at room temperature

200 g of sugar

4 large egg yolks

1 whole eggs

3/4 tsp. vanilla extract

2 tsp. brown rum

For frosting:

1 large egg yolk

1 Tbsp. milk

1/3 tsp. Fleur de Sel

1. Butter or oil a pie plate about 25 cm with removable background and preheat the oven to 350°F.
2. Mix together the buckwheat flour, wheat flour, salt and cinnamon.
3. By hand or mixer, beat the butter until it is light and frothy. Add the sugar and continue to beat until the mixture is homogeneous.
4. In a mixing bowl, beat with a fork the 4 egg yolks and the whole egg with vanilla and rum. 
5. Vigorously beat into the butter mixture.
6. Gently fold in the dry ingredients until just combined.
7. Evenly level the dough in the pie plate.
8. For the frosting, beat the egg yolk with the milk using a fork and brush on top of the cake. With a fork draw stripes as in the photo.
9. Sprinkle the top of the cake with the 1/3 tsp. of salt and bake for 45 minutes. Let cool completely before unmolding.