Preheat oven to 400°F and line a baking sheet with parchment paper.
In a large bowl, whisk flour, sugar, baking powder, baking soda, salt and lemon zest. Set aside.
Grate frozen butter into flour mixture. Using your hands, work in the butter until the texture resembles a coarse meal.
Fold blueberries into dry ingredients.
In a separate small bowl, whisk sour cream and egg until completely smooth. Gently stir into dry ingredients until just combined being careful not to squish the blueberries. Be sure not over work the dough. Form the dough into a ball. It will be sticky and crumbly at first but will come together as you form it.
Place dough on a lightly floured surface and lightly pat into an 8" circle about ¾" thick. Use a very sharp knife to cut into 8 triangles (like a pizza). Transfer triangles onto prepared baking sheet placing them 2-3 inches apart.
Bake for 15-17 minutes or until the tops begin to golden slightly. Don't take them out too early or the texture will be too soft. Allow them to cool for 10 minutes on the pan before transferring onto a wire rack to finish cooling completely.