One key to flaky, tender scones is the ingredients you use, but another is the temperature of those ingredients. Using chilled butter—and mixing everything together quickly, before it warms up—helps create those perfect flaky layers. Using frozen berries helps keep the dough’s temperature low. It also prevents the bright berry color from bleeding out of the berries and into the dough. If you don’t like mixed berries, you can use 1 cup (5 ounces) of frozen raspberries, blueberries, or blackberries instead of the mixed berries. Berry Scones Makes 8 scones 1 cup (5 ounces) frozen mixed berries 1 tablespoon confectioners’ (powdered) sugar 1 1/2 cups (7 1/2 ounces) all-purpose flour, plus extra for counter 6 tablespoons unsalted butter, cut into 1/2 inch pieces and chilled 2 tablespoons sugar 1 1/2 teaspoons baking powder 1/2 teaspoon salt 1/2 cup (4 ounces) whole milk 1 large egg yolk Adjust the oven rack …