Taken from The Complete America's Test Kitchen Tv Show Cookbook.
"It is important to work the dough as little as possible - work quickly and knead and fold the dough only number of times called for. The butter should be frozen sold before grating ... If fresh berries are unavailable, an equal amount of frozen berries, unthawed, can be substituted. An equal amount of raspberries, blackberries, or strawberries can also be used in place of the blueberries ... Refrigerate or freeze leftover scones, wrapped in foil, in an airtight container."
16 tablespoons (2 sticks) unsalted butter, frozen whole
11/2 cups fresh blueberries
1/2 cup whole milk
1/2 cup sour cream
2 cups flour
1/2 cup sugar
2 teaspoons baking powder
1/2 teaspoon table salt
1/4 teaspoon baking soda
1 teaspoon grated zest from 1 lemon
one) Adjust an oven rack to the middle position and heat oven to 425 degrees. Score and remove half of the wrapper from each stick of frozen butter. Grate the unwrapped ends on the large holes of a grater (you should grate a total of 8 tablespoons). Place the grated butter in the freezer until needed. Melt 2 tablespoons of the remaining ungrated butter and set aside. Save the remaining 6 tablespoons of butter for another use.
two) Whisk the milk and sour cream together in a medium bowl; refrigerate until needed. Whisk the flour, 1/2 cup of the sugar, the baking powder, salt, baking soda, and lemon zest together in a medium bowl. Add frozen butter to the flour mixture and toss with your finger until the butter is thoroughly coated.
three) Add the milk mixture to the flour mixture; fold with a rubber spatula, transfer the dough to a liberally floured work surface. Dust the surface of the dough with flour; with floured hands knead the dough 6 to 8 times, until it just holds together in a ragged ball, adding flour as needed to prevent sticking.
four) Roll the dough into an approximate 12-inch square. Fold the dough into thirds like a business letter, using a spatula to release the dough if it sticks to the work surface. Lift the short ends of the dough and fold into thirds again to form an approximate 4-inch square. Transfer the dough to a plate lightly dusted with flour an chill in the freezer for 5 minutes.
five) Transfer the dough to a floured work surface and roll into an approximate 12 inch square again. Sprinkle the blueberries evenly over the surface of the dough, then press down so they are slightly embedded in the dough. Roll the dough, pressing to form a tight log. Lay the log seam side down and press it into a 12 by 4 inch rectangle. Using a sharp, floured knife, cut the rectangle crosswise into 4 equal rectangles. Cut each rectangle diagonally to form 2 triangles and transfer to a parchment lined baking sheet.
six) Brush the tops with melted butter and sprinkle with 1 tablespoon sugar. Bake until tops and bottoms are golden brown, 18 to 25 minutes. Transfer to a wire rack and cool for 10 minutes before serving.