Preheat oven to 425 F. Lightly coat a cookie sheet with cooking spray and set aside.
Combine dried cherries and boiling water in a saucepan and boil. Let stand for 10 minutes to rehydrate cherries. Drain and set aside.
In a large bowl, sift together flour, sugar, cornmeal, baking soda, and salt. Cut in butter using a pastry blender until mixture is like coarse meal.
Combine drained cherries, yogurt, milk, vanilla, and egg. Gradually add flour to mixture and combine until moistened. Do not over mix. Batter will be a little sticky, but if too sticky to handle, add a little flour.
Turn dough onto cookie sheet. Using a knife or bench scraper, score into eight wedges. Brush top with egg white wash and sprinkle with sugar.
Bake for 20 minutes or until golden.