Preheat oven to 425F. Adjust the rack to the middle.
Grate 8 tablespoons of butter on a large holed box grated. Place grated butter & blueberries in the freezer.
Melt 2 tablespoons butter. Set aside.
Whisk milk & sour cream together in medium bowl. Put in refrigerator until needed.
Whisk flour, 1/2 cup sugar, baking powder, baking soda and lemon zest together. Add grated butter from the freezer and toss together until butter is thoroughly coated with flour.
Add milk mixture to the flour mixture and combine together with spatula.
Sprinkle working surface with flour, then transfer the dough on top of it. Dust the top of the dough with flour as well. Flour your hands and kneed dough 6-8 times, until it just comes together in a ragged ball, dusting with flour as needed to prevent sticking.
Roll dough into a 12 inch square, then fold dough 3 times, to the shape of a business letter. Now lift short ends of dough and fold towards the middle, making a 4 inch square. Transfer dough to a floured plate and place in the freezer for 5 minutes.
Remove dough from freezer to floured work surface and roll it to a 12 inch square again. Sprinkle blueberries evenly over dough and press down with hands to embed into the dough.
Using a metal spatula, loosen dough from work surface and roll it into a log, seam down. Shape it into 12x4 rectangle. Using a sharp floured knife, cut rectangle into 4 equal rectangles. Cut each rectangle diagonally into 2 triangles. Transfer to a parchment or foil lined baking sheet.
Brush tops of each scone with melted butter and liberally sprinkle with sugar.
Transfer to oven and bake until tops and bottoms are golden brown, about 18-25 minutes. Remove from oven and let cool for 10 minutes on a cooling rack before serving.
To make ahead:
Once the scones are shaped, place on a baking sheet and refrigerate or freeze overnight. When ready to bake the refrigerated scones, brush with butter, sprinkle with sugar and bake in a preheated to 425F oven18-25 minutes.
For previously frozen scones, preheat oven to 375F, brush the scones with butter, sprinkle with sugar and bake for 40-50 minutes.