For the cupcakes:

1. Preheat the oven to 350°F. Line a cupcake pan with cupcake liners.
2. In a large mixing bowl, combine the sugar, vegetable oil, eggs, and vanilla extract. Beat on medium speed until the eggs and oil are well incorporated and the batter is lighter in color, about 2 minutes. Scrape down the bowl as needed.
3. Next mix in the sour cream and beat until well combined.
4. Add half the flour followed by the baking powder and salt, and beat on low speed while pouring in half of the milk and mix just until the flour starts to incorporate.
5. Finally add the remaining flour, mixing on low speed while pouring in the remaining milk and beating until all of the ingredients are well combined.
6. Use a spatula to scrape down the sides of the bowl and stir the batter from the bottom to the top to ensure it’s well mixed.
7. Using a large cookie scoop, divide the batter evenly, filling each liner 2/3 full. Careful not to overfill.
8. Bake at 350°F for 14-16 minutes. Test the cupcakes for doneness by inserting a toothpick into the center of the cupcake. If the toothpick comes out clean, the cupcakes are done. Cool Completely.

For the frosting:

1. Cut the butter into pieces. Using the paddle attachment, whip the butter for 5-7 minutes, scraping down the bowl occasionally, and beating until the butter look light in color.
2. Add 2 cups of powdered sugar and mix on low speed until incorporated into the butter then add the vanilla extract and mix to combine. Beat for about 60 seconds.
3. Next, add an additional 2 cups of powdered sugar and beat on low speed until sugar is incorporated. Increase speed to medium-high and beat for 3 minutes.
4. Add the last 1 cup of powdered sugar along with the heavy whipping cream. Beat on low until the ingredients start to mix together. Increase speed to medium-high and beat for another 3-5 minutes to whip additional air into the frosting.