Whole Wheat Rhubarb Scones

Bahan-bahan (8 porsi)

• 1/2 cup unsalted butter ((1 stick) at room temperature)
• 2 cups whole wheat flour ((or white whole wheat if you prefer a milder taste))
• 2 tablespoons granulated sugar
• 2 teaspoons baking powder
• 1 teaspoon ground cinnamon
• 1/2 teaspoon baking soda
• 1/2 teaspoon kosher salt
• 1/2 cup rhubarb (diced (or the fruits, nuts, and/or chips of your choice))
• 1/2 cup cold buttermilk (plus 2 tablespoons (plus 1 additional tablespoon as needed))
• 3 tablespoons boiled cider ((see notes))
• 1 large egg (separated)
• Sparkling sugar (optional)