Demerara Sugar Buns

Name: Demerara Sugar Buns
Ingredients: 1 ¼-ounce envelope active dry yeast (about 2¼ teaspoons); ⅔ cup whole milk, warmed; 3 tablespoons pure maple syrup; 2 large eggs, room temperature; ¾ teaspoon kosher salt; 1 cup whole wheat flour; 2¾ cups all-purpose flour, plus more; 6 tablespoons unsalted butter, room temperature, cut into 1-inch pieces, plus melted for brushing (about 4 tablespoons); ⅓ cup granulated sugar, plus more; 5 dried juniper berries (optional); ⅓ cup demerara sugar, plus more