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. Next, mix in the sour cream and beat until well combined.
3. In a separate bowl, combine the remaining dry ingredients: flour, baking powder,r and salt. Add half the dry ingredients and half of the milk and mix just until the flour starts to incorporate. Add the remaining ingredients and mix until 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.
4. Using a large cookie scoop, divide the batter evenly, filling each liner 2/3 full. Careful not to overfill.
5. 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 Filling:

1. In a medium-sized saucepan, combine the blackberries with the sugar and flour. Stir well. Then add the lemon juice, bourbon, and mint leaves. Cook over medium-high heat until mixture starts to break down and is lightly boiling with bursting bubbles on the top. Reduce heat and simmer for another 5 minutes, stirring occasionally, until the blackberry sauce starts to thicken.
2. Remove from heat and allow the sauce to cool completely, refrigerating to help speed up the process. The sauce will thicken more as it cools.
3. Once the filling has cooled, cut out the center of the cupcake using a knife or a cupcake corer. Fill the center of the cupcake with blackberry sauce. Set the leftovers aside.

For the Frosting:

1. Cut the butter into pieces, about 1 tablespoon size. Using the paddle attachment, whip the butter for 3-5 minutes, scraping down the bowl occasionally. Beat the butter until it fluffy and whipped, easily spreadable.
2. Alternate slowly adding the powdered sugar, 1 cup at a time, with the liquid ingredients, mixing on low speed until it’s incorporated into the butter. Then increase the speed to high and beat for 30-60 seconds.  Repeat until all your powdered sugar and liquid ingredients have been added. Once all the ingredients have been added, beat at a high speed for about 2-3 minutes until the frosting is light and fluffy.
3. In a large piping bag fitted with a large open round tip, pipe the frosting onto the cupcakes.
4. Garnish with leftover blackberry sauce before serving, top with a fresh blueberry and a mint leaf. Keep these in an airtight container.