1 - In a large bowl, whisk together 1/2 cup buckwheat flour, 2/3 cup all-purpose flour, 1/2 teaspoon salt, and 1 teaspoon yeast.

2 - Make a well in the center and pour in 1 cup warm milk, whisking until the batter is smooth.

3 - Cover the bowl and let the batter rise until doubled, about 1 hour.

4 - Enrich and Rest the Batter Stir 2 tablespoons melted butter and 1 egg yolk into the batter.

5 - In a separate bowl, whisk 1 egg white until stiff, but not dry.