In a large bowl, stir together 2 1/4 cups flour, sugar, baking powder, salt, baking soda, and cream of tartar, and set aside. In a small bowl, stir together the buttermilk, sour cream, egg, and vanilla extract. This will not become completely smooth- that's okay. Place it in the fridge until needed. 

Cut the cold butter into the flour mixture using a pastry blender or your hands, working quickly, until you have a crumbly mixture with small chunks of butter running throughout. 

Using a fork, mix in the wet ingredients until the dough comes together. It should be a little sticky, but still workable. If the dough is too wet, add in another tablespoon or two of flour. If it's too dry and crumbly, add in another tablespoon of buttermilk. 

Turn the dough out onto a floured surface and pat it into a rectangle. Mix together the additional sugar and the cinnamon until combined, and sprinkle about half of it onto the rectangle. Then, fold it into thirds by folding the short ends into the middle. This should form a dough rectangle about 3 inches by 8 inches. (you don't have to measure). 

Cut the dough into eight squares by cutting it once down the middle lengthwise, and then into quarters widthwise. Place the squares onto a small baking sheet or plate, and pop them in the freezer for about 20 minutes. 

Meanwhile, preheat your oven to 425 degrees, and line a large baking sheet with parchment paper. Sprinkle 8 little piles of sugar onto the baking sheet, one for each scone. The scones will bake on top of these, and it creates a sweet, cinnamony, crust. 

Once the scones have chilled, place each one on top of a pile of the cinnamon-sugar mixture. Then, brush the tops with a little more buttermilk, and generously sprinkle the remaining cinnamon-sugar mixture over the tops. 

Bake the scones for about 15-18 minutes, or until they are puffy and deeply golden brown. Cool and enjoy!