Preheat oven to 375ºF / 180ºC. Line baking sheets with parchment paper.

In the bowl of a food processor, put flour, sugar, baking powder, cornstarch and salt. Process few seconds just to mix (around 10 seconds).

Alternatively, you can mix everything in a large bowl, from all the dry ingredients to wet ingredients. Add the wet ingredients gradually until the dough starts to come together.

Scatter butter and orange zest over this mixture, and pulse a few times until the butter is the size of peas.

Transfer into a large mixing bowl (if using food processor) and gradually pour buttermilk and mix everything until most of it is moist enough to make the mixture to clump together.

Dump it onto the kitchen counter and quickly give it a few turns to avoid very dry spots. Do not over mix.

Form it into a disk, about 5 (thicker scones) or 6 inch diameter, cut in quarters and stack each portion on top of each other. Gently press down and re-shape into a 5-6 inch disk.

Freeze for at least 30 minutes up to 1 hr before baking.

Cut the scones into 8 (if making a large batch) or 4 (if making a small batch) and arrange them on the baking sheets lined with parchment paper.

Brush top with additional buttermilk or for better browning, brush the top with egg wash (1 beaten egg + 1 teaspoon water).

Bake for about 20-25 minutes or until top turned golden brown and the scones are puffed up and tall.

Cool in a wire rack. Serve as is or with a dusting of icing sugar.

Mix icing sugar, orange juice and zest of orange for the glaze. Stir until smooth.

Drizzle the glaze on top of the cooled scones.