Preheat oven to 375°.

Line a baking sheet with parchment paper.

In a large bowl, combine flour, sugar, baking powder, and salt, whisking well. Using a pastry blender, cut butter into flour mixture until it resembles coarse crumbs.

In a medium bowl, combine cream, prepared tea, egg, and egg yolk, whisking to blend. Add to flour mixture, stirring until mixture is evenly moist. (If mixture seems dry, add more cream, 1 tablespoon at a time.) Bring mixture together with hands until a dough forms.

On a lightly floured surface, gently knead dough until smooth. Using a rolling pin, roll dough to a ¾- to 1-inch thickness. Using a 2½-inch round cutter, cut 12 scones from dough, rerolling scraps as necessary. Place scones approximately 2 inches apart on prepared baking sheet.

In a small bowl, lightly beat egg white. Brush scones with egg white.

Garnish tops of scones with a sprinkle of turbinado sugar, if desired. Bake until lightly browned, 15 to 18 minutes.