Preheat oven to 375 degrees F. Grease pan; set aside. Beat egg with buttermilk and set aside. In a large bowl, stir together flour, baking powder, baking soda, and salt. Add butter, cutting with a pastry blender or rubbing with your fingers, until mixture resembles coarse meal. Lightly stir in blueberries and sugar. Stir in buttermilk mixture with a fork until a soft dough forms. Turn out dough onto a lightly floured surface and knead 5 times. Separate dough into eight equal pieces and press into each cavity of the pan. Bake 20-25 minutes or until medium brown. Let cool 20 minutes in pan. Remove from pan and cool completely.