Preheat oven to 400 degrees. Line a baking sheet with a silicone baking sheet or parchment paper.
In a large mixing bowl, sift and combine the flour, baking powder, baking soda, sugar, brown sugar, salt, and cinnamon. Set aside.
Separate the egg yolk from the white. Save the yolk for the last step before baking.
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)
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.
Using a large ice-cream scoop, scoop the dough out onto the baking sheet. I used a half cup scoop size.
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.
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.
Reduced fat sour cream, 5%, has a thinner consistency and works much better in this recipe than full fat sour cream. The thin consistency is needed to bind all of the other ingredients together.
If making the lemon poppy seed scone, use only 1 heaping tablespoon of poppy seeds as the add-in. Also, add the lemon zest from one large lemon to the dry ingredients before mixing with the wet ingredients.
To make the glaze, combine 1 cup of confectioner's sugar with 2 tablespoons of lemon juice. Whisk together well. Drizzle over completely cooled scones.