Heat oven to 400 degrees F. Line a baking sheet with parchment paper.
In a large bowl, whisk together flour, baking soda, cream of tartar, salt and
the 6 tablespoons sugar.
Add butter to the flour mixture and use your fingertips
to rub it into the flour, breaking the butter down into pieces smaller than a pea.
Combine milk and vanilla extract in a small bowl and add about 6 tablespoons
to flour mixture. Stir with a fork until dough comes together into a slightly sticky
ball. If necessary, add additional tablespoon or two of milk. Dough should not be
too wet. Divide dough into six even balls.
In a small bowl, whisk together the 1/4 cup sugar and ground cinnamon.
Roll each ball of scone dough in the cinnamon sugar mixture and flatten slightly
onto prepared baking sheet.
Bake for about 15 minutes, until scones are set and edges begin to brown.