To start, ensure that your ingredients are cold, as this is key to achieving tender scones. Begin by grating or finely dicing the frozen butter into pea-sized pieces. This step is crucial because cold butter helps create the flakiness in the scone dough. Once grated, place the butter back in the freezer while you gather and prepare the remaining ingredients.

In a large mixing bowl, whisk together the flour, cornstarch, granulated sugar, baking powder, and salt. It is important to mix up the flour mixture separately from the other ingredients first to be sure that all of the ingredients are fully incorporated and won't clump up when adding the wet ingredients.

Remove the frozen butter from the freezer and add it to the flour mixture. Using a fork or a pastry blender, cut the butter into the dry ingredients until the butter pieces are slightly smaller than the size of a pea. The key is to work quickly to keep the butter cold, which will help create those desired flaky layers in your scones.

Next, add the cold potato flake sourdough starter, vanilla extract, and cold heavy cream to the dry ingredients in the mixing bowl. Stir gently until a dough forms, being careful not to overwork it. Just before the dough is fully combined, fold in the chocolate chips. The scone dough should come together fairly easily but should not be over-mixed to ensure tender scones.

Dust the dough lightly with flour and then wrap the dough ball tightly in plastic wrap. Refrigerate it for at least 30 minutes. Chilling the dough helps relax the gluten, firms up the butter, and develops the flavors. For optimal flavor development and fermentation benefits, you can refrigerate the dough overnight for 8-12 hours, or even up to 24 hours if desired.

After the dough has chilled, preheat your oven to 400°F (200°C). Turn the dough out onto a clean surface, and avoid adding additional flour if possible. Flatten the dough into a circle about one inch thick. Using a bench scraper or a knife, cut the dough into 8 equal pieces. This step ensures that each scone bakes evenly and achieves the best results. This recipe makes large scones, if you want smaller scones you can just cut into more pieces to make the scone size you desire.

Transfer the scone wedges to a parchment-lined baking sheet, leaving about 2 inches of space between each scone. Place the baking sheet in the freezer for 5-10 minutes while the oven finishes preheating. This quick freeze helps the scones retain their shape and rise better during baking. Once the oven is ready, remove the baking sheet from the freezer and bake the scones on the middle oven rack for 15-20 minutes or until they are golden brown on top.

While the scones are baking, prepare the glaze. In a small bowl, combine the melted butter, powdered sugar, vanilla extract, and milk. Adjust the consistency to your preference by adding more or less milk. Aim for a drizzling consistency that will zig-zag over the tops of the scones beautifully.

Once the scones are done baking, transfer them to a wire rack to cool slightly before glazing. Use a spoon to drizzle the glaze over the top of the scones. For those with a sweet tooth, feel free to add more glaze to your liking.