In a bowl, stir together the flour, salt, cream of tartar and baking soda.
In a mixer bowl, cream the butter and sugar.
Add the eggs and mix.
Add the milk and vanilla and mix until well combined.
Stir the wet ingredients into the dry ingredients, just until moistened.
Fill muffin cups 2/3 of the way full of batter.
Sprinkle with cinnamon sugar. I just pinched some between my fingers and sprinkled the top of each muffin.
Bake at 400 degrees for 15-20 minutes, or until a toothpick comes out clean.