Preheat oven to 400º. Grease 9×13 pan. In large bowl, combine flour, sugar, baking powder, and salt. Add butter and cream cheese and mix just to combine. Dough will be lumpy. Add egg and buttermilk and mix 2-3 minutes until dough forms a ball. Add blueberries. With floured hands, pat dough into prepared pan. Bake 10 minutes. Reduce oven temperature to 375º and continue baking 15 minutes or until golden brown. Remove from oven and cool 10 minutes. Cut into 16 servings and serve warm.