Preheat your oven to 350°F (175°C). Line a cupcake pan with liners and set aside.
In a large mixing bowl, cream together the unsalted butter and granulated sugar using an electric mixer until the mixture is light and fluffy—about 3-5 minutes.
Add the eggs one at a time, mixing well after each addition. Then, add the vanilla extract and dried vanilla beans, mixing until fully incorporated.
Add the sour cream and milk to the mixture, stirring gently until everything is well combined.
In a separate bowl, whisk together the all-purpose flour, baking powder, baking soda, and salt.
Gradually add the dry ingredients to the wet mixture, mixing just until combined. Be careful not to overmix; a few flour streaks are perfectly fine.
Using a scoop or spoon, fill each cupcake liner about two-thirds full with batter.
Bake in the preheated oven for 18-20 minutes, or until a toothpick inserted into the center comes out clean.
Allow the cupcakes to cool in the pan for 5 minutes before transferring them to a wire rack to cool completely.
In a mixing bowl, beat together the softened butter and powdered sugar. Add 1-2 tablespoons of milk and the vanilla, mixing until you reach a smooth and creamy consistency. Adjust with more milk if necessary.
Once the cupcakes are completely cool, frost them with your desired amount of frosting. You can use a piping bag for a fancy touch or simply spread it on with a knife.
