01 - Preheat oven to 400°F. Line baking sheet with parchment paper.
02 - Whisk together all-purpose flour, whole wheat flour, sugar, baking soda, baking powder, and salt in large bowl.
03 - Add cold butter cubes. Rub into flour mixture with fingertips or pastry cutter until coarse crumbs form.
04 - Stir in currants until evenly distributed throughout flour mixture.
05 - Whisk buttermilk and egg together in separate bowl. Pour into dry ingredients.
06 - Stir gently just until shaggy dough forms. Do not overmix.
07 - Turn dough onto lightly floured surface. Pat into 1-inch thick round. Cut into 8 wedges.
08 - Transfer wedges to prepared baking sheet, spacing slightly apart.
09 - Brush tops with buttermilk and sprinkle with coarse sugar if desired.
10 - Bake 18-20 minutes until golden brown and toothpick inserted in center comes out clean.
11 - Cool on wire rack. Serve warm or at room temperature.