Combine flours, baking powder, and sugar in a bowl. Cut in butter until mixture resembles fine crumbs. Beat cream and egg yolk together and add to dry ingredients. Stir with a fork just until dry ingredients are moistened.

Gently fold in blueberries with rubber scraper. Turn out on a floured surface and knead gently about six times to form a ball. Pat dough into a circle about 3/4-inch thick. Carefully place on greased baking sheet. Mark off eight wedges with a sharp knife. Be careful not to cut all the way through. Sprinkle with sugar. Bake for 20 minutes or until browned.

Break into wedges and serve hot with butter.