These are a very refreshing treat to have on a summer day! If you like key lime pie, you will love these!! They are nice for something different as far as cupcakes go:) It is important to have real Key Lime juice, instead of just regular lime juice!
In a mixing bowl, cream butter and sugar on high speed, until light and fluffy, about 5 minutes. On low speed, add eggs, one at a time, mixing well after each one. Add vanilla, lime zest, and juice and mix well.
In another bowl, sift together flour, baking powder and soda, and salt. In 5 parts total alternately add dry ingrediants and buttermilk to butter, beginning and ending with dry. Mix until just combined.
Line muffin tins with paper and fill each liner about 3/4 full.
Bake for 25 minutes until tops are slightly browned and a toothpick inserted comes out clean. Remove and cool in pan for 10 minutes. Transfer to a wire rack to cool completly.
In a small glass bowl, set over a pot of simmering water. Slowly melt white chocolate. Remove and let cool until slightly warm.
In a mixing bowl, beat butter until light and fluffy. On low speed, gradually add confectioners sugar until mixed.
Add salt, vanilla, lime juice, and sour cream and mix well.
Add melted white chocolate and mix just until incorporated.
Frost cupcakes and garnish with grated lime zest. Can refrigerate, but don't have to.