Preheat oven to 350F (176C) and prepare a cupcake pan with cupcake liners; set aside.
In a large mixing bowl, cream the butter and sugar together until light in color and fluffy; about 3 to 4 minutes.
Add the vanilla extract and sour cream and mix until well combined.
Add 1 of the egg whites and mix until combined.
Add the remaining 2 egg whites and mix until well combined.
Scrape down the sides of the bowl as needed to be sure all ingredients are well incorporated.
Combine the flour and baking powder in a medium bowl, and combine the milk and water in a small measuring cup.
Add half of the flour mixture to the egg mixture and mix until integrated.
Add the milk mixture and mix until combined.
Add the remaining half of the flour mixture and mix until well combined and smooth, scraping down the sides and bottom of the bowl as needed.
Fill the cupcake liners with the prepared batter about halfway up.
Bake the cupcakes for 15 to 17 minutes, or until a toothpick inserted comes out with a few crumbs.
Remove the cupcakes from the oven and allow them to cool for 2 to 3 minutes, then remove them from the pan and transfer them to a cooling rack to finish cooling.
To finish the cranberries, remove them from the simple syrup and roll them in the remaining 1/4 cup of sugar. You may need to roll them a few times to get a couple layers of sugar on them.
Set the cranberries aside to dry for an hour or so.