Preheat oven to 425 degrees. Lightly grease cookie sheet.
Combine first 6 ingredients in medium bowl.
Cut butter into flour mixture until is resembles coarse meal. Add lemon or orange zest. Add buttermilk and knead until dough leaves the sides of bowl.
Place dough on floured board and pat into about an 8 inch diameter circle. Transfer to the lightly greased cookie sheet. Cut into 6-8 wedges, but do not separate. Brush top lightly with milk, and sprinkle with a small amount of chai powder.