Preheat your oven to 350 degrees. Line and grease two 12-cup muffin pans.
In a bowl cream butter and sugar until light and fluffy.
Add eggs and egg yolks, one at a time, mixing thoroughly.
Add zest, lime juice, and vanilla, mix.
Using a spatula, scrape the sides and bottom of the bowl. Turn the mixer on for another 30 seconds.
Combine flour, baking powder and soda, and salt in a bowl.
Mixing on low, alternate adding large scoops of the flour mixture and the buttermilk, beginning and ending with the flour.
Once you have added the last of your flour, remove the bowl from the mixer and mix gently by hand until combined (may look slightly bumpy but that's ok). Fold in blueberries.
Spoon batter into muffin cups until 2/3 full. Gently tap the pan to remove air bubbles.
Bake at 350 degrees for about 17 minutes or until a knife comes out clean.
Allow to cool completely before frosting.
To make the frosting beat all the frosting ingredient in a bowl on low until mixed.
Increase your mixer speed to medium high and whip until smooth, about 4 minutes.
Pipe frosting onto cooled cupcakes and top with fresh blackberries and lime zest.
Serve immediately or store in an airtight container at room temperature for up to 2 days.