Preheat oven to 350°F (175°C). Line a muffin tin with cupcake liners.
In a medium bowl, whisk together flour, baking soda, cream of tartar, and salt.
In a large bowl, cream together butter and sugar until light and fluffy. Beat in eggs one at a time, then stir in vanilla.
Gradually add the dry ingredients to the wet ingredients, alternating with the sour cream, beginning and ending with the dry ingredients. Mix until just combined.
Fill cupcake liners about 2/3 full. Sprinkle with cinnamon sugar.
Bake for 18-20 minutes, or until a toothpick inserted into the center comes out clean.
Let cool in the muffin tin for a few minutes before transferring to a wire rack to cool completely.
Notes
These cupcakes are best served fresh. Store leftovers in an airtight container at room temperature for up to 3 days.