01 - Preheat the oven to 400°F. Line a baking sheet with parchment paper.
02 - In a large bowl, whisk together the all-purpose flour, whole wheat flour, sugar, baking soda, baking powder, and salt until well blended.
03 - Add the cold butter cubes to the flour mixture. Using your fingertips or a pastry cutter, work the butter into the flour until the mixture resembles coarse crumbs with some pea-sized pieces remaining.
04 - Stir in the currants until evenly distributed throughout the flour mixture.
05 - In a separate bowl, whisk together the buttermilk and egg until combined.
06 - Pour the wet ingredients into the dry ingredients. Stir gently with a spatula or wooden spoon just until combined. The dough will be shaggy and slightly sticky. Do not overmix.
07 - Turn the dough out onto a lightly floured surface. Gently pat it into a round disk about 1 inch thick. Handle the dough minimally to keep it tender.
08 - Cut the disk into 8 equal wedges using a sharp knife or bench scraper. Transfer the wedges to the prepared baking sheet, spacing them about 2 inches apart.
09 - Brush the tops of the scones with the additional buttermilk using a pastry brush. Sprinkle evenly with coarse sugar.
10 - Bake for 18 to 20 minutes, or until the tops are golden brown and a toothpick inserted into the center of a scone comes out clean.
11 - Let the scones cool on the baking sheet for 5 minutes, then transfer to a wire rack. Serve warm or at room temperature with butter and jam.