Line a rimmed baking sheet with parchment paper and set it aside.
In a large mixing bowl, whisk together the flour, granulated sugar, matcha powder, baking powder, and salt for a full 30 seconds to break up any clumps.
Add the cold, cubed butter to the dry ingredients. Use a pastry cutter or your fingers to work the butter into the flour until the mixture looks like coarse crumbs with some pea sized pieces of butter remaining.
In a separate small bowl, whisk together the heavy cream, egg, and vanilla extract until fully combined.
Make a well in the center of the dry ingredients and pour in the wet mixture. Use a rubber spatula or your hands to fold the dough together just until no dry flour remains. Do not overmix.
Turn the dough out onto a lightly floured surface and gently pat it into a disc about 3/4 to 1 inch thick. Use a bench scraper or sharp knife to cut the disc into 8 even wedges.
Transfer the wedges to your prepared baking sheet, spacing them about 2 inches apart. Refrigerate for 15 minutes while you preheat the oven to 400 degrees Fahrenheit.
Remove the baking sheet from the fridge and brush the tops of each scone with a little extra heavy cream. Sprinkle with coarse or turbinado sugar. Bake for 16 to 18 minutes until risen and lightly golden on the bottoms.
Let the scones rest on the baking sheet for 5 minutes, then transfer to a wire cooling rack and cool for another 10 minutes before glazing.
In a small bowl, whisk together the powdered sugar and matcha powder. Add the heavy cream one tablespoon at a time, whisking until you reach a smooth, pourable consistency.
Drizzle or spoon the glaze over the cooled matcha scones. Let the glaze set for a few minutes before serving.