Preheat the oven to 350°F. Line a cupcake pan with cupcake liners.
In a large mixing bowl, combine the sugar, vegetable oil, eggs and lemon 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.
Next, add the lemon zest and the sour cream and beat until well combined.
Combine the dry ingredients in a separate bowl. Add half the dry ingredients followed by the lemon juice and half the buttermilk and mix just until the flour starts to incorporate.
Finally add the remaining dry ingredients and buttermilk and beat until all of the ingredients are well combined.
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.
Using a large cookie scoop, divide the batter evenly, filling each liner 2/3 full. Careful not to overfill.
Bake at 350°F for 15-18 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:
Cut the butter into pieces. Using the paddle attachment, whip butter for 5-7 minutes, scraping down the bowl occasionally. Beat until butter look light in color.
Add 2 cups of powdered sugar and mix on low speed until incorporated into butter then add the lemon extract and lemon zest and mix to combine. Beat for about 60 seconds.
Next, add an additional 2 cups of powdered sugar and the buttermilk and beat on low speed until sugar is incorporated. Increase speed to medium-high and beat for 3 minutes.
Add last 1 cup powdered sugar along with the heavy cream. Beat on low until ingredients start to mix together. Increase speed to medium-high and beat for another 3-5 minutes to whip additional air into the frosting.
Use a large open star tip to frost these cupcakes. Top with a slice of lemon or fresh berries.