Maple-Oatmeal Scones

INGREDIENTS

• 4½ cups all-purpose flour
• 1 cup quick-cooking oats, plus additional for sprinkling
• 2 tablespoons baking powder
• 2 tablespoons granulated sugar
• 2 teaspoons salt
• 1 pound (4 sticks) cold unsalted butter, diced
• ½ cup cold buttermilk
• ½ cup pure maple syrup
• 4 extra-large eggs, lightly beaten
• 1 egg beaten with 1 tablespoon milk or water, for egg wash
• :
• 1¼ cups confectioners' sugar
• 1 teaspoon pure vanilla extract