Preheat the oven:

Preheat your oven to 350°F (175°C) and line a cupcake tin with cupcake liners.

Mix the dry ingredients:

In a medium bowl, whisk together the flour, baking powder, baking soda, and salt. Set aside.

Cream the butter and sugar:

In a large bowl, use an electric mixer or whisk to beat the softened butter and sugar together until light and fluffy, about 2-3 minutes.

Add the eggs and vanilla:

Beat in the eggs one at a time, mixing well after each addition. Stir in the vanilla extract.

Combine wet and dry ingredients:

Add half of the dry ingredients to the butter mixture and mix until just combined. Then add the sour cream and milk, followed by the remaining dry ingredients. Mix until the batter is smooth, but do not overmix.

Fill the cupcake liners:

Divide the batter evenly among the cupcake liners, filling each about 2/3 full.

Bake:

Bake for 18-20 minutes, or until a toothpick inserted into the center of a cupcake comes out clean. Let the cupcakes cool in the tin for 5 minutes, then transfer them to a wire rack to cool completely.

Make the frosting:

In a large bowl, beat the softened butter until creamy. Gradually add the powdered sugar, one cup at a time, mixing well after each addition. Add the vanilla extract, heavy cream (or milk), and a pinch of salt. Beat until the frosting is smooth and fluffy.

Frost the cupcakes:

Once the cupcakes are completely cooled, frost them with the buttercream using a spatula or a piping bag for a decorative touch.

Decorate and serve:

Add sprinkles, edible pearls, or other decorations if desired. Serve and enjoy!