Preheat oven to 375!. Mix flour, baking powder, soda, orange peel and salt. Cut in the butter with a pastry blender until the mixture resembles coarse crumbs. In a separate bowl, toss currants in sugar. Add to dry ingredients. Mix well. In small bowl, mix egg yolk and buttermilk and pour into flour mixture just to blend. Turn dough onto lightly floured surface. Knead with hands and roll into 11! circle. Cut into wedges and place on lightly greased baking sheet. Bake for 20-25 minutes or until lightly browned. Do not overbake. When cool, drizzle with powdered sugar icing.