01 - Preheat oven to 400°F. Line a baking sheet with parchment paper.
02 - In a large bowl, whisk together all-purpose flour, whole wheat flour, sugar, baking soda, baking powder, and salt until well blended.
03 - Add cold butter cubes to the flour mixture. Using a pastry cutter or fingertips, work butter into flour until mixture resembles coarse crumbs with some pea-sized pieces remaining.
04 - Stir dried currants into the flour-butter mixture until evenly distributed.
05 - In a separate bowl, whisk together cold buttermilk and egg until thoroughly combined.
06 - Pour buttermilk mixture over dry ingredients. Stir gently with a fork until just combined; dough should be slightly sticky but hold together. Do not overmix.
07 - Turn dough onto lightly floured surface. Pat into a 1-inch thick circle. Cut into 8 equal wedges and transfer to prepared baking sheet, leaving space between pieces.
08 - If desired, sprinkle tops with demerara or turbinado sugar for extra crunch and sweetness.
09 - Bake for 18 to 20 minutes until golden brown and a toothpick inserted into the center comes out clean.
10 - Cool slightly on wire rack. Serve warm or at room temperature with salted butter and jam.