• Preheat the oven to 350° (325° if you are making a cake instead of cupcakes). Line 2 cupcake pans with liners and grease or grease and flour your cake pans (1 9x13 pan or 2 9-inch round pans).
• In a stand mixer bowl, add the cake flour, all-purpose flour, sugar, baking powder, baking soda, and salt. Stir on low speed to combine.
• Add the softened butter, mixing on med/low until the mixture resembles damp sand (about 1 minute).
• Add the eggs, one at a time, scraping the sides and bottom of the bowl to be sure all of the ingredients are fully incorporated.
• Add the sour cream, milk, and vanilla and stir until fully combined.

For Cupcakes:

• Fill the cupcake cups half full of batter and bake for 16-20 minutes or until a toothpick inserted in the middle comes out clean or with a few moist crumbs.
• Remove from the oven and cool on a cooling rack.

For Cake:

• Pour the batter into the prepared pan, level the top with a spatula, and bake for 20-40 minutes at 325° or until a toothpick inserted in the middle comes out clean or with only a few crumbs.
• Remove from the oven and cool on a rack.