To make the cupcakes:

1. Prepare a cupcake pan with cupcake liners. Preheat oven to 350°F (176°C).
2. Combine the flour, baking powder, baking soda and salt in a medium sized bowl and set aside.
3. Add the butter, oil, and sugar to a large mixer bowl and beat together until light in color and fluffy, about 1 1/2 to 2 minutes. Do not skimp on the creaming time.
4. Add the vanilla extract and sour cream and mix until well combined.
5. Add the eggs one at a time, mixing until mostly combined after each. Scrape down the sides of the bowl as needed to be sure all ingredients are well incorporated.
6. Add half of the dry ingredients to the batter and mix until mostly combined.
7. Combine the lemon juice, lemon zest and milk then slowly add the mixture to the batter and mix until well combined.
8. Add the remaining dry ingredients and mix until well combined and smooth. Scrape down the sides of the bowl as needed to be sure all ingredients are well incorporated. Do not over mix the batter.
9. Toss the blueberries with 1/2 a tablespoon of flour and gently toss to combine, then add the blueberries to cake batter and fold to combine.
10. Add the batter to the cupcake liners, filling a little more than half way full. Bake 17-20 minutes, or until a toothpick inserted into the center comes out clean.
11. Remove cupcakes from the oven and remove to a cooling rack to cool completely.

Make the frosting and assemble:

1. Combine the cream cheese and butter and mix until well combined and smooth.
2. Add about half of the powdered sugar and mix until well combined and smooth.
3. Add the vanilla extract, lemon extract and lemon zest and mix until well combined and smooth.
4. Add the remaining powdered sugar and mix until well combined and smooth.
5. Use a large piping tip to pipe the frosting onto the cupcakes. I used Ateco tip 847.
6. Top the cupcakes with a quarter of a lemon slice and a blueberry, if desired. Refrigerate until ready to serve and serve at room temperature. Cupcakes are best if eaten within 3-4 days.