Heat oven to 425°F with rack set in middle position. Line a baking sheet with parchment paper; set aside.

Grate 4 tablespoons frozen butter on a large-hole grater; transfer to a bowl and freeze. Place blueberries in freezer until needed.

Whisk together milk and Greek yogurt; refrigerate.

Whisk flour, sugar, baking powder, baking soda, salt, and lemon zest in medium bowl.

Add frozen butter to flour mixture and toss with fingers until thoroughly coated.

Add milk mixture to flour mixture and, using a spatula, fold until just combined. Transfer dough to a well-floured work surface. Dust dough with flour and knead until it forms a rough ball, 8 to 10 times, adding flour as needed to prevent sticking.

Roll dough out into a rough 12-inch square. Fold dough into thirds (like a letter). Lift ends of dough and fold into thirds again to form a 4-inch square. Transfer dough to plate lightly dusted with flour and freeze 5 minutes.

Remove dough from freezer and transfer to floured work surface. Roll out into a 12-inch square.

Sprinkle blueberries evenly over surface of dough and lightly press into dough.

Using a bench scraper, carefully release dough from surface. Roll to form a tight log, jelly roll style. Arrange dough log seam-side down and press into a 12x4-inch rectangle. Using a sharp knife, cut log crosswise into 4 equal sections. Cut each rectangle diagonally to form 2 triangles. Transfer scones to parchment-lined baking sheet.

Melt remaining 2 tablespoons of butter and lightly brush tops of scones. Lightly sprinkle with turbinado sugar.

Bake scones until tops and bottoms are golden brown, 20–25 minutes. Transfer to wire rack and cool completely.