Grate or finely dice frozen the butter into pea-sized pieces. Place the bowl of butter in the freezer while you gather and prepare the remaining ingredients.
In a small bowl use a zester to remove the zest from the oranges. In a separate bowl juice the oranges. Set aside the zest and juice for later use.
Remove the butter from the freezer and add it back to the mixing bowl. To the bowl, add the flour, sugar, baking powder, salt, cornstarch, and half of the orange zest. Use a fork or a pastry cutter to cut in the butter until the chunks of butter are slightly smaller than the size of a pea.
Add the potato flake sourdough starter, cold heavy cream, and ¼ cup of the orange juice to the dry ingredients in the mixing bowl. Stir until a dough forms, being careful not to overwork it. The dough should come together easily but should not be over-mixed.
Wrap the dough ball tightly in plastic wrap and refrigerate it for at least 30 minutes so that the dough gets cold. For optimal flavor development and fermentation benefits, you can refrigerate the dough overnight for 8-12 hours. Even up to 24 hours if desired.
After the refrigeration time, preheat the oven to 400 degrees Fahrenheit. Turn the dough out onto a clean surface, avoid adding additional flour if at all possible. Flatten it into a circle about one inch thick.
Cut the dough into 8 equal pieces and transfer them to a parchment-lined baking sheet, leaving about 2 inches of space between each scone. Place the baking sheet into the freezer for 5-10 minutes while the oven finishes preheating.
Once the oven is preheated, remove the baking sheet from the freezer and place in the oven immediately. Bake the scones on the middle oven rack for 15-20 minutes or until they are lightly browned.
While the scones bake prepare the glaze. In a small bowl, combine the melted butter, powdered sugar, remaining orange zest, and enough orange juice to achieve the desired consistency. Aim for a drizzling consistency, adding approximately ¼ cup of orange juice.
Once the scones are done, allow them to cool on a wire rack before icing.
To glaze, use a spoon to pour a small amount of glaze on top of the scones. Use the back of the spoon to spread the glaze over the top of the scones, adding more glaze to achieve personal preference.
These scones are best enjoyed fresh, but if there are any remaining, store in an airtight container at room temperature for up to three days. If keeping them longer than that, you will want to wrap them tightly in plastic wrap and freeze them for optimal freshness.