Preheat the oven to 375 degrees F (190 C). Grease a large baking sheet or line it with parchment paper.
In a large bowl, whisk together the flour, sugar, salt, baking powder, and baking soda.
Cut the butter into small cubes and add it to the dry ingredients. Using a pastry blender or your hands, cut the butter into the dry ingredients until it resembles coarse crumbs.
In a small bowl, whisk together the egg and buttermilk. Add this to the dry ingredients and mix with a fork until just combined (the dough will be very wet).
Fold in the orange zest and blueberries. Turn the dough out onto a lightly floured surface and shape it into a rectangle shape about 1 inch thick. Cut the dough into 8 wedges and place on the prepared baking sheet.
Bake for 25-30 minutes or until golden brown. Let cool before glazing with the orange juice and powdered sugar. Cut it into any shape you like & serve.