Place the flours, sugar, baking powder and salt into a food processor. Pulse a couple of times to combine. Add butter. Pulse until mixture resembles coarse meal (about 8-10 times).
Add buttermilk, rind, and lemon juice. Pulse until just combined.
Scrape dough onto a lightly floured surface. Sprinkle top of dough lightly with flour (dough will be soft). Pat dough into an 8-inch circle.
Cut dough into 10 wedges. Brush wedges with egg white and sprinkle with a teaspoon of sugar.
Bake for 25 minutes or until golden. Cool on a wire rack. Great with lemon curd or your favorite jam and lots of butter.