From Cook’s Illustrated
16 tablespoons (2 sticks) butter, frozen whole
1 ½ cups fresh blueberries, freeze before use
½ cup whole milk
½ cup sour cream
2 cups unbleached all-purpose flour, plus additional for work surface
½ cup sugar, plus additional for sprinkling (you can also use turbinado sugar or sanding sugar)
2 teaspoons baking powder
½ teaspoon baking soda
½ teaspoon salt
1 teaspoon finely grated zest from 1 lemon
- Adjust oven rack to middle position and heat oven to 425 degrees.
- To grate butter, score and remove half of wrapper from each stick of frozen butter. Grate unwrapped ends on large holes of box grater (you should grate 8 tablespoons). Place grated butter in freezer until needed. Melt 2 tablespoons of remaining ungrated butte and set aside. Save remaining 6 tablespoons of butter for another use.
- Place blueberries in freezer until needed.
- Whisk together milk and sour cream in medium bowl; refrigerate until needed.
- Whisk flour, ½ cup 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; fold with spatula until just combined. With rubber spatula, transfer dough to liberally floured work space. Dust surface with flour; with floured hands, knead dough 6 – 8 times, until it just holds together in ragged ball, adding flour as needed to prevent sticking.
- Roll dough into approximate 12-inch square. Fold dough into thirds like a business letter, using bench scraper or metal spatula to release the dough if it sticks to countertop. Lift short ends of dough and fold into thirds again to form approximate 4-inch square. Transfer dough tot plate lightly dusted with flour and chill in freezer for 5 minutes.
- Transfer dough to floured work surface and roll into approximate 12-inch square again. Sprinkle frozen blueberries evenly over surface of dough, then press down so they are slightly embedded in dough. Using bench scraper or 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-inch rectangle. Using sharp, floured knife, cut rectangle crosswise into 4 rectangles. Cut each rectangle in half then cut diagonally to form 2 triangles and transfer to parchment-lined baking sheet.
- Brush tops with melted butter and sprinkle with sugar. Bake until tops and bottoms are golden brown, 18 – 25 minutes. Transfer to wire rack and let cool 10 minutes before serving.