#For_the_Cupcakes:

Preheat oven to 375F. Line the cupcake tin with papers.
Add the sugar and lemon zest to the bowl of a food processor then pulse until zest is broken up and the sugar is pale yellow In color.
Sift the flour, baking soda, baking powder and salt into a large bowl then whisk together and set aside.

Add the eggs, milk, melted butter, lemon juice, sour cream, and sugar to a medium bowl and whisk together.

#For_the_Buttercream:

Cream the butter, salt and zest for a few minutes then sift in the powdered sugar in a few batches, mixing in between.
Scrape the bowl down and pour In the lemon juice while mixing on low. Scrape down once more and mix then transfer to a piping bag and decorate the cooled cupcakes.

NEVER use bottled lemon juice! It really will not taste the same.
You can substitute whole milk yogurt for the sour cream if desired, I do it all the time and can’t really tell the difference.
If you're using lemon zest for garnish then add just before serving. It will dry out fairly quickly.