reheat oven to 350 F (175 C).
Remove seeds from the vanilla bean.
Combine sugar and vanilla bean seeds in a bowl.
Add butter, eggs, sour cream, milk, and vanilla extract
Add cake flour, baking powder, baking soda, and salt.
Mix until just combined.
Fill cupcake liners just over 3/4 full.
Bake for 15 minutes and then test to see if they are done. They are done when a toothpick comes out without wet batter stuck to it. The cupcakes should appear white with specks of vanilla bean. They should not turn a golden brown. If they are not done, test again in two minutes. If they are still not done, test again in another two minutes.
When the cupcakes are done, remove them immediately from the tins and leave them on a cooling rack.