Preheat the oven to 350 degrees F.
Add cupcake liners to two (12-count) cupcake pans.
Make sure to set the cold ingredients out, so they can come closer to room temperature before making the batter. This will keep the batter from clumping up and will help it mix better.
In a medium-sized bowl, combine the flour, baking powder, baking soda and salt. Whisk well and set aside.
In another bowl, add the sour cream, milk, and vanilla extract. Whisk well and set aside.
In a large mixing bowl, add the room-temperature butter, oil and the sugar and mix with an electric mixer on medium-high for several minutes until light and fluffy.
Add the eggs one at a time and mix on low-medium for about 15-20 seconds after adding each egg.
Scrape down the sides and bottom of the bowl and mix again on medium speed for another 10 seconds.
Add half the dry ingredients to the butter and sugar mixture. Mix only on low-medium speed and only until everything is just combined and you don’t see any dry flour.
Add the liquid ingredients and mix on low-medium speed only until just combined.
Add the second half of the dry ingredients and mix on low-medium speed until just combined.
Use a silicone spatula and scrape down the sides and the bottom of the bowl, then use the spatula to mix the batter just a bit more by hand to finish mixing without the electric mixer.
The goal is to try and use the electric mixer the least amount that is needed. If scratch cake batter is mixed too long or at too high of speed, the cupcakes will turn out dense and rubbery and may fall in the middle.
Add the batter to the cupcake liners. Fill each about ⅔ of the way full. Be careful not to overfill the cupcake liners or it makes the cupcakes more cumbersome to get out of the pan and they may end up very flat on top. The batter may be a little thick when you add to the cupcake liners.
Bake at 350 degrees F on the middle rack for approximately 14 - 18 minutes.
Do not overbake, or the cupcakes can turn out dry. These cupcakes are finished baking when they are firm on the top, are light golden brown and a toothpick inserted into a couple of them, comes out when either a few moist crumbs or clean.
Remove the cupcakes from the oven and set the pans on a cooling rack for about 10 minutes. The tops of the cupcakes will level out a bit as they sit.
After about 10 minutes, lift the cupcakes out of the pans and set them onto the cooling rack to cool completely before adding frosting. Be very careful when lifting them out of the cupcake pan as the cupcakes are quite delicate.
Once the cupcakes are cool, cover with buttercream or your choice of topping. See notes for a link to my favorite buttercream recipe.