Preheat oven to 200 degrees F. Place the cherries on a parchment-lined baking sheet and bake for 30 minutes. Cherries will appear drier and a bit wrinkly. Set aside.
In a medium bowl, mix together all-purpose flour, buckwheat flour, sugar, baking powder and salt. Using a box grater, grate the cold butter into the flour mixture. Working quickly, and using your hands, mix the butter into the flour mixture until it resembles a coarse meal. Gently stir in the cherries and chocolate, being sure to coat them in the flour mixture.
Pour in 1/2 cup of heavy cream and mix until the dough begins to form. Add a tablespoon at a time until the dough forms a ball. I needed about 2 tablespoons, so the end measurement was 1/2 cups of heavy cream, plus 2 tablespoons. Transfer the dough and all dry, floury bits to a liberally floured countertop and knead the dough by hand just until it reaches a slightly sticky mass, 5 to 10 seconds. Pat the dough to a 1/2-inch thickness. You can cut the scones into 8 wedges or you can use a biscuit cutter. I did the latter and rerolled the scraps to get 8 circular scones. Place the scones on a parchment-lined baking sheet. Transfer to the freezer to chill for 10 minutes. While the scones are in the oven, preheat it to 400 degrees F.
Before placing them in the oven, brush the tops' of the scones with the egg wash and sprinkle with the turbinado sugar. Transfer to the oven and bake until the scones are lightly browned, 12 to 15 minutes. Cool on a wire rack for at least 10 minutes. Serve warm or room temperature with butter.