Line an 11-by-17-inch baking sheet with parchment paper. Combine all dry ingredients with cherries, if using, in the bowl of an electric mixer fitted with a paddle attachment. Add butter, and mix on medium-low speed until mixture resembles coarse meal. Add buttermilk, and mix until combined.
Turn out mixture onto a clean work surface. With hands, quickly pat mixture into a 16-by-3 1/2-inch rectangle that is 1 1/2 inches high. Score rectangle into ten triangles. Cover with plastic wrap, and transfer to the freezer for at least 2 hours.
Heat oven to 350 degrees. Remove dough from the freezer, and cut into triangles with a sharp knife. Place scones 2 inches apart on the prepared baking sheet. Brush scones with heavy cream, and sprinkle with sugar. Bake until lightly golden, about 30 minutes.
Freezing the dough for at least two hours before baking keeps scones from spreading too much. The dough will keep in the freezer for up to three weeks.