Working quickly, dice the cold butter into small, even cubes, place it on a plate, and freeze it while preparing the remaining ingredients.
Measure the heavy cream into a 2-cup liquid measuring cup, whisk in 1 whole egg and 1 egg yolk, reserve the remaining egg white for brushing, and place the cream mixture in the freezer to chill.
Add the flour, granulated sugar, baking powder, chai spice blend, and kosher salt to a food processor and pulse several times to combine.
Add the frozen butter and pulse 25 to 30 times, stopping when some butter pieces are finely coated with flour and several larger pieces remain visible.
Gradually pulse in the chilled cream and egg mixture until the dough begins forming a rough ball and pulling away from the sides of the food processor; do not add more liquid than needed.
Transfer the dough to a lightly floured surface, gather it gently into a ball, press it into a thick disc, wrap it in plastic, and freeze it for 30 minutes.
Preheat the oven to 375°F and line a large baking sheet with parchment paper or a silicone baking mat.
For full-sized scones, roll or press the chilled dough into a 1-inch-thick circle and cut it into 8 wedges with a sharp knife or bench scraper.
For mini scones, roll the dough into a 1/2-inch-thick rectangle, cut it into 2-inch-wide strips, and divide each strip into triangles about 2 inches wide and 3 inches long.
Arrange the scones on the prepared baking sheet with space between them and brush the tops generously with the reserved egg white.
Bake for 20 to 22 minutes, checking mini scones a few minutes early, until the tops are golden, the centers are puffed, and the edges are lightly crisp.
Transfer the baked scones to a wire rack and allow them to cool before glazing.
While the scones bake, whisk together the powdered sugar, chai spice blend, vanilla extract, heavy cream, maple syrup, and kosher salt until a thick glaze forms.
Adjust the glaze with additional powdered sugar if it is too thin or add heavy cream 1 teaspoon at a time if it is too thick.
Dip the top of each cooled scone into the glaze, allow the first coating to settle for several minutes, and dip the scones a second time for a thicker finish.
Let the glaze set for about 10 minutes before serving the scones with coffee or tea.