Preheat oven to 350° F. Sift together flour, baking soda, baking powder and sea salt; set aside. In a small bowl, combine mango purée, lime juice and zest, and buttermilk; set aside. In a mixing bowl, cream butter until fluffy. Add agave; mix well. Add eggs, one at a time. Add half of the reserved dry ingredients to the butter mixture; mix on low until just combined. With mixer running on low, slowly add the mango mixture. Add remaining dry ingredients until just combined. Fill paper-lined muffin tins 2/3 full. Bake 18-22 minutes, or until a toothpick inserted in center of a muffin comes out clean. Remove to wire rack; cool. Frost with Mango Lime Buttercream frosting and sprinkle with additional sea salt and nonpareils, if desired.

MANGO LIME BUTTERCREAM FROSTING:
In a mixing bowl, cream butter until light and fluffy. Add mango purée, lime juice and zest, and agave; mix well. Add powdered sugar, 1 cup at a time, until desired spreading consistency.