Preheat the oven to 350ºF and line a muffin tin with cupcake liners. (Use blue liners if you want to mimic the ocean.)
In a large bowl, sift together the flour, baking powder and salt. Set it aside.
In a liquid measuring cup, stir together the coconut milk, egg whites and vanilla extract. Set it aside.
In the bowl of a stand mixer fitted with the paddle attachment, cream together the butter and sugar until light and fluffy, about 3 minutes. Alternately add the dry and wet ingredients in 3 increments, starting and ending with the dry ingredients. Beat the batter just until combined, scraping down the sides as needed.
Stir in the coconut then divide the batter equally into 12 cups in the muffin tin. Bake the cupcakes for 25 to 30 minutes until a toothpick inserted comes out clean. Let the cupcakes cool for 5 minutes in the pan then transfer them to a rack to cool completely. While the cupcakes are cooling, make the frosting and pretzel palm trees.