Preheat the oven to 325 degrees F. Place cupcake liners into cupcake pans.
In a separate bowl combine the cake flour, baking powder and salt. Whisk 30 seconds to blend. Set aside.
In another bowl combine the sour cream, vanilla extract, vegetable oil, and milk. Stir and set aside.
Add butter to mixing bowl and mix on low to medium speed until smooth.
Slowly add the white and brown sugar mixing on MEDIUM speed until the mixture has lightened in color and is fluffy- Approximately 3 minutes.
Next, add the eggs one at a time, mixing after each each addition until yolk is blended.
With the mixer on low speed, add the dry ingredients alternately with the wet ingredients beginning and ending with the dry ingredients. Stop and scrape down the sides of bowl once or twice as need. After the last addition of dry ingredients, mix just until blended.
Add the cupcake batter to the cupcake pans (prepared with liners). Each cupcake will have approximately ¼ cup batter. Bake for 18-20 minutes or until a toothpick can be inserted and removed with no crumbs or just a few moist crumbs attached.
Makes approximately 7.5-8 cups of batter- enough for 28-30 cupcakes.