Preheat your oven to 325 degrees Fahrenheit. Prepare your muffin tins by lining them with paper liners, making it easier to remove the cupcakes once baked.
In a large mixing bowl, combine the all-purpose flour, baking powder, baking soda, and salt. Whisk these dry ingredients together until well combined. This step ensures an even distribution of the leavening agents throughout the flour.
In a liquid measuring cup, combine the milk and a touch of vanilla. Stir this mixture together and set it aside. This helps the flavors meld together nicely.
In another large bowl, use a mixer to cream together the softened butter, vegetable oil, and sugar. Beat them until the mixture becomes light and fluffy. This process typically takes about three to four minutes.
Now, add in the eggs and egg whites one at a time, ensuring each is well incorporated before adding the next. This step is key to achieving a smooth batter.
Once the mixture is fluffy and well combined, alternate adding in the dry flour mixture with the milk mixture. Start and end with the flour, mixing just until combined. Be careful not to overmix, as this can lead to dense cupcakes.
Using a scoop, fill each cupcake liner about three-quarters full with batter. This allows room for the cupcakes to rise without spilling over.
Place the muffin tin in the lower two-thirds of the preheated oven and bake for 18 to 20 minutes. The cupcakes are done when a toothpick inserted into the center comes out clean or has a few moist crumbs.
Once baked, allow the cupcakes to cool in the muffin tins for 15 to 20 minutes. Afterward, carefully invert them onto cooling racks to cool completely before frosting and decorating.
