Preheat oven to 350°F. Lightly grease a large baking sheet.
In a small mixing bowl, stir together sour cream and baking soda. Set aside.
In a large bowl, cream together butter and sugar until light and fluffy.
In a small bowl, beat together egg and vanilla and beat into butter/sugar mixture. Stir in sour cream mixture.
In a large bowl, mix together remaining dry ingredients: flour, baking powder, cream of tartar and salt. Add to wet ingredients and stir until just moistened.
Turn out onto a lightly floured surface and need for 2 to 3 minutes, until dough comes together. Pat dough out into a circle 3/4" thick. Cut into 16 wedges and place them on prepared baking sheet.
Bake for 12 to 15 minutes in the preheated oven until the bottoms are golden brown.
Notes
Cinnamon raisin: Add 1 1/2 tsp cinnamon and 1 cup raisinsLemon poppyseed: Add 1/2-1 tsp lemon extract or zest from 2 lemons and 1 1/2 tbsp poppyseedCheesy ham and onion: Reduce sugar to 1/4 cup and omit vanilla. Add 3/4-1 cup chopped cooked ham, 1/2-3/4 cup chopped green onion and 1/2-3/4 cup grated Cheddar.