1. Preheat oven to 425 F (220 C). Line a large baking sheet with parchment paper or a silicone mat or butter it.
2. Grind whole rye berries into flour. In a medium mixing bowl, whisk together the flour, baking powder, sugar, soda, and salt. Cut butter in 1/4-inch (1 cm) slices and drop into flour mixture. Use a pastry blender or two table knives to cut butter into flour mixture until mixture resembles coarse crumbs.
3. Add buttermilk and fold together with a rubber spatula until evenly mixed and a soft dough forms. If it is too dry, drizzle a little more buttermilk over it as you fold.
4. Working quickly, and handling the dough gently for maximum rise, drop rounded spoonfuls of dough from greased spoon onto the prepared cookie sheet about 1 inch (2.5 cm) apart. Recipe should make about 1 dozen biscuits, depending on size.
5. Bake until lightly browned and done, about 10-12 minutes. Serve warm.