Warm the oven to 350°F (176°C) and prep your cupcake pan with liners, delicious things are about to happen!

Using a medium bowl, stir together the flour, baking powder, baking soda, and salt until fully combined. Set it aside for now, we’ll come back to it shortly.

In a large bowl, beat the butter, sugars, and peanut butter with a hand or stand mixer until light and pale. This should take about 4 minutes. The fluffier it gets, the lighter your cupcakes will be, so take your time with this step!

Then, mix in the sour cream and vanilla extract until well combined. The sour cream gives these cupcakes that perfect moistness, and the vanilla adds that sweet, comforting flavor.

Crack in the egg and then the yolk, blending well between each to ensure a smooth batter. Slowly add half of your dry ingredients to the wet ingredients. 

Stir gently to combine, but don’t overmix. Then add the milk and mix until it’s smooth. Don’t worry if it looks a little curdled at first, that’s totally fine!

Stir in the rest of the dry ingredients, mixing until everything comes together without overworking the batter. You’re aiming for a smooth, creamy batter, no lumps allowed!

Take a moment to scrape the bowl and make sure all the ingredients are evenly combined.

Fill each cupcake liner with batter, aiming for a halfway full portion. Don’t overfill, as these cupcakes rise nicely.

Bake for about 15 minutes, but do the toothpick test, insert it into the center of a cupcake, and if it comes out clean, they’re done. If needed, let them bake for a minute or two longer until fully set.

Cool the cupcakes in the pan for approximately five minutes, then transfer them to a wire rack. Make sure they’re completely cool before frosting.

Begin the peanut butter buttercream by creaming the butter until it's perfectly smooth and soft. This will give your frosting that soft, rich texture.

Add the peanut butter and continue mixing until everything is well combined and creamy.

Add in half of the powdered sugar gradually, mixing thoroughly until the frosting is perfectly smooth and lump-free.

Add the vanilla extract, salt, and a few tablespoons of milk to help smooth it all out. This will help the frosting have the perfect consistency for spreading and piping.

Beat in the remaining powdered sugar until the frosting is light, smooth, and fluffy. If it’s too dense, simply add a little more milk until it reaches the perfect consistency.

Once your cupcakes are completely cool, frost them generously with that dreamy peanut butter buttercream. Enjoy!