Heat the oven to 425°F (220°C) and line a baking sheet with parchment. Whisk together the flour, granulated sugar, baking powder, and salt in a large bowl.

Cut the cold butter into the dry ingredients with a pastry blender or your fingertips until coarse crumbs form, leaving a few pea-sized pieces visible. Whisk the egg and heavy cream together in a separate bowl, then add them to the flour mixture.

Stir just until a shaggy dough forms, then turn it onto a lightly floured surface. Fold or knead the dough only a few times before patting it into an approximately 8-inch round about 1 inch thick.

Cut the dough into eight wedges and transfer them to the prepared baking sheet. For taller scones, chill the shaped wedges for about 15–30 minutes before baking.

Bake for 12–15 minutes, until the tops are lightly golden and the centers are set. Let the scones cool for several minutes while you prepare the glaze.

Whisk the confectioners’ sugar, seeds from half a vanilla bean, and enough cream, milk, or half-and-half to make a thick but pourable glaze. Drizzle it over the warm or cooled scones and serve.