It is important to work the dough as little as possible—work quickly and knead and fold the dough only the number of times called for. The butter should be frozen solid before grating. In hot or humid environments, chill the flour mixture and workbowls before use. While the recipe calls for 2 whole sticks of butter, only 10 tablespoons are actually used. If fresh berries are unavailable, an equal amount of frozen berries (do not defrost) can be substituted. An equal amount of raspberries, blackberries, or strawberries can be used in place of the blueberries. Cut larger berries into 1/4- to 1/2-inch pieces before incorporating.

Adjust oven rack to middle position and heat oven to 425°. Remove half of wrapper from each stick of butter and grate unwrapped ends on large holes of box grater, grating a total of 8 tbs.) Place grated butter in freezer until needed. Melt 2 tablespoons of remaining butter and set aside. Save remaining 6 tablespoons for future use. Place blueberries in freezer until needed.

Whisk together milk and sour cream in med bowl; refrigerate unil needed. Whisk flour, sugar, baking powder, baking soda, salt and lemon zest in med bowl. Add frozen butter and toss with fingers until thoroughly coated.

Add milk mixture to flour mixture; fold with spatula until just combined. With rubber spatula, transfer dough to liberally floured work surface. Dust surface of dough with flour and knead dough with floured hands 6 to 8 times, until it just holds together in ragged ball, adding flour as needed to prevent sticking.

Roll dough into approximate 12-in square. Fold dough into thirds like a business letter, using scraper to release dough if it sticks. Lift short ends of dough and fol into thirds again to form approximate 4-in square. Transfer dough to plate lightly dusted with flour and chill in freezer 5 minutes.

Tranfer dough to floured work surface and roll into approximate 12-in square again. Sprinkle blueberries evenly over surface of dough, then press down so they are slightly embedded in dough. Using thin metal spatula, loosen dough from work surface. Roll dough, pressing to form tight log. Lay seam-side down and press log into 12 by 4-in rectangle. Using sharp, floured knife, cut rectangle crosswise into 4 equal rectangles. Cut each rectangle diagonally to form 2 triangles and transfer to parchment-lined baking sheet.

Brush tops with melted butter and sprinkle with remaining tablespoon sugar. Bake until tops and bottoms are golden brown, 18 to 25 minutes. Transfer to wire rack and let cool 10 minutes before serving.

Makes 8. Refrigerate or freeze leftover scones, wrapped in foil, in an airtight container. To serve, remove foil and place scones on a baking sheet in a 375-degree oven. Heat until warmed through and recrisped, 8 to 10 minutes if refrigerated, 16 to 20 minutes if frozen.