Step 1

Preheat oven to 375F. Line the cupcake tin with papers.

Step 2

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.

Step 3

Sift the flour, baking soda, baking powder and salt into a large bowl then whisk together and set aside.

Step 4

Add the eggs, milk, melted butter, lemon juice, sour cream, and sugar to a medium bowl and whisk together. Everything should be room temperature, but If things clump up after mixing then just microwave the bowl for 30 seconds and mix once more.

Step 5

Add the wet to the dry mixture and mix until just combined. Fill cupcake papers about 3/4 the way up. Bake for 5 min at 375F then reduce temperature to 350F and bake another 10-12 or until the springy to the touch.

Step 6

Cream the butter, salt and zest for a few minutes then sift in the powdered sugar in a few batches, mixing in between.

Step 7

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.