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 lemon extract. Beat on medium speed until the eggs and oil are well incorporated. Scrape down the bowl as needed.
3. Next, zest 2 lemons and then juice the lemons. Set the lemon juice aside and add the zest and sour cream to the batter, beating until well combined.
4. Combine the remaining dry ingredients in another bowl. Add half of the dry ingredients, the lemon juice, and half of the buttermilk and mix just until the flour starts to incorporate. Then add the remaining dry ingredients and buttermilk. 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.
5. Using a large cookie scoop, divide the batter evenly, filling each liner 2/3 full. Careful not to overfill. 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. Puree the blackberries using a food processor. Optional, strain the blackberry puree through a fine sieve to make a smoother frosting. Set aside.
2. Set your bowl over top of a pot with water, just enough to cover the bottom of the pot. You do not want the water to boil and touch the bottom of your mixing bowl. Heat the water on medium to medium-low heat.
3. Combine the sugar and egg whites in your mixing bowl and stir (using your greaseproof spatula) constantly until the mixture reaches 140° F. This is the most important part; you do not want to egg whites to cook. When it reaches 140° F, the sugar should be dissolved in the egg whites. You can test this by placing a drop on your fingertips and rubbing them together. The mixture should be completely smooth.
4. Place the mixing bowl on your stand mixer. Using the wire whisk attachment, beat the egg whites. Start on low and increase the speed to medium after 2 minutes.
5. Beat for another 3 minutes on medium. At this point, your frosting should have turned white as the egg whites are whipped and the body of the meringue starts to form.
6. After 5 minutes, increase the speed to high. You will notice that as you increase the speed, the body of your meringue will also increase. It will start to look glossy as the peaks begin to form. Beat for another 5 minutes.
7. After you have beat the meringue for a total of about 10 minutes, the bottom of your mixing bowl should be cooled completely. Your SMB should look kind of like whipped cream. Scrape down all sides and bottom of the bowl.
8. Turn your mixer down to medium-low. Slowly add your butter, about 1 tablespoon at a time, ensuring it is mixed well after each addition. Once you have added all your butter. Mix for another minute and scrape down the sides of the bowl.
9. Switch to the paddle attachment and continue beating on medium to allow all the air bubbles to escape. In about 2-3 minutes the frosting is smooth.
10. Lastly, fold in the blackberry puree and lemon zest and stir well to combine. Use a large piping bag fitted with a large open round tip to pipe the cooled cupcakes.