Preheat oven to 375ºF / 180ºC. Line baking sheets with parchment paper.
Dry Ingredients: In the bowl of a food processor, put flour, sugar, baking powder, cornstarch and salt. Process few seconds just to mix (around 10 seconds).
Manual: 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.
Add Butter & Orange Zest: Scatter butter and orange zest over this mixture, and pulse a few times until the butter is the size of peas.
Alternatively, you can use a large cheese grater, or a pastry cutter.
Buttermilk: 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. You may NOT need to use all the buttermilk, so it is important to add it gradually. STOP when you are able to form a ball out of the dough.
Shape: Dump it onto the kitchen counter and quickly give it a few turns to avoid very dry spots. Do not over mix,the more you touch it and mix it, the tougher the baked scones will be. Stop once it starts to clump together. Form it into a disk, about 5 (thicker scones) or 6 inch diameter, cut in quarters and stacks each portion of top of each other. Gently press- down and re-shape into a 5-6 inch disk. The stacking will help create layers in the scones.
Chill: Freeze for at least 30 minutes up to 1 hr before baking. The freezing will help lessen the spreading and will produce a thcker scones.
Cut: Cut the scones into 8 (if making a large batch or 4 if making a small batch) arrange them on the baking sheets lined with parchment paper.
Brush Top: 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 puff-up and tall. Rotate the pan half way the baking time. This helps even baking of the scones.
Tip: If baking a frozen scone straight from the oven, bake for 25 – 30 minutes or until top turned golden brown and rise.
Cool in a wire rack. As this stage, you can serve this as is o with a dusting of icing sugar. If you are galzing it, make sure the scone is completely cooled.
Make the Glaze: Mix icing sugar, orange juice and zest of orange. Stir until smooth. If you want a thicker glazed, just add more sugar.
Drizzle: Drizzle the glaze on top of the cooled scones
Re-heating: Re-heat in a 300F for 10 -15 minutes. If you have the sugar glaze on top, expect that this will melt. I suggest adding glaze only to the one that you are consuming for the day.
Storage: Scones are best served the day they are made but if you have leftover, cover and store in room temperature (away from sunlight) for 3 days, more than that it is best kept in refrigerator. If you plan to eat it for few days, I suggest add the glaze on top so you can re-heat the scone when you want to it eat.