Preheat oven to 350 degrees. Prep 6 wells in a muffin tin with liners.
In a large bowl, cream butter, sugar and zest. Add the egg yolk and mix thoroughly.
Add the flour, baking powder and salt to the butter mixture.
Add the sour cream and juice to the rest of the batter and beat till well combined.
Fill each cupcake well 2/3 full.
Bake for 12 to 15 minutes, do a toothpick test, if it comes out clean with just a couple of crumbs, remove them from the oven to cool briefly on a wire rack, then remove from the pan to cool completely before icing.
Beat the egg whites and a pinch of salt, to form soft peaks using an electric mixer.
Meanwhile, in a medium saucepan bring sugar, tangerine slices, juice and water to a boil, stirring occasionally.
Continue to boil until it reaches a soft ball stage (when a drop of syrup forms a soft ball when dropped in cool water) while continuing to stir occasionally.
Keep the mixer running, you'll need an extra set of hands.
While you pour a continuous stream of the molten syrup into the egg whites, continue to beat for about 5 minutes or until frosting is fluffy, glossy and cool.
Allow the tangerine slices to cool and harden on a wire rack.
Frost the cooled cupcakes and top with candied tangerine slices.
NOTE: IF THE ICING ISN'T ORANGE ENOUGH IN COLOR, YOU CAN ADD A DROP OR TWO OF FOOD COLORING.