Preheat oven to 425°F.
Combine flour, sugar, baking powder, baking soda, and salt in a food processor bowl with steel blade and blend for 8 seconds (or whisk together in a large bowl.)
Cut in butter by pulsing 8 times with food processor (or use a pastry cutter), until mixture resembles coarse meal. Do not over blend.
Whisk egg with buttermilk. Add egg mixture to dry mix in food processor and pulse just until dough comes together (or create a well in dry ingredients, add egg mixture and stir just until moistened). Stir in currants.
Turn dough onto floured surface and pat into 8-inch circle, approximately ½ to ¾-inch thick. Cut into wedges or cut with 3-inch biscuit cutter and place on a parchment lined or buttered baking sheet. Brush with buttermilk. Bake 15-18 minutes or until golden brown. Serve warm, spread with lots of Challenge Butter.