1-Preheat oven to 400 degrees: Preheat oven to 400 degrees. Line a baking sheet with a silicone baking sheet or parchment paper.
2-In a large mixing bowl, sift and: In a large mixing bowl, sift and combine the flour, baking powder, baking soda, sugar, brown sugar, salt, and cinnamon. Set aside.
3-Separate the egg yolk from the white: Separate the egg yolk from the white. Save the yolk for the last step before baking.
4-In another bowl, whisk together the egg: In another bowl, whisk together the egg white, melted butter, and sour cream. (If you are adding an extract – vanilla or anything else, add it now, but no more than 2 teaspoons)
5-Once mixed, add the dry ingredients, and: Once mixed, add the dry ingredients, and your add-in, to the wet ingredients and stir until most of the ingredients have come together. DO NOT over mix the dough. Mix just until the flour is incorporated.
6-Using a large ice-cream scoop, scoop the: Using a large ice-cream scoop, scoop the dough out onto the baking sheet. I used a half cup scoop size.
7-Add one tablespoon of water to the: Add one tablespoon of water to the egg yolk and whisk to combine. Using a pastry brush, lightly brush the top of each scone with the egg yolk mixture. Sprinkle over about a half teaspoon of course sugar, if using.
8-Bake for 15 minutes: Bake for 15 minutes. Remove from oven and immediately remove from baking sheet and transfer to a wire cooling rack. Serve warm or at room temperature.