Preheat the oven to 350 degrees F and line 2 cupcake pans with papers.
Place the flours, sugar, baking powder, baking soda, lemon zest, and salt in a large mixing bowl, and mix on low speed to combine.
Add the butter, stirring on low speed until the mixture resembles damp sand (about a minute).
Add the eggs, one at a time, scraping the sides and bottom of the bowl with a silicone spatula, to be sure all of the ingredients are combined.
Add the pineapple puree, coconut milk, and coconut extract, and mix on medium-high speed for about a minute and a half, to build the cake’s structure and aerate the batter.
Place about ¼ cup of batter in each well of the cupcake pans, and bake the cupcakes for 16-18 minutes, or until they spring back when lightly pressed and a toothpick inserted in the center comes out clean or with a few moist crumbs.
Cool completely and top with buttercream.
To Make the Buttercream*:
Place the egg whites and sugar in a large metal mixing bowl and whisk together.
Set the bowl over a small pot of simmering water, and heat, whisking occasionally, until the mixture becomes translucent and no longer feels gritty when rubbed between the thumb and forefinger.
Remove from heat and whip on high speed until the meringue holds stiff peaks.
Cool completely (There should be no hint of warmth when the hand is place on the side of the bowl. Place in the refrigerator for 10-20 minutes, if necessary.)
Add the butter, a tablespoon at a time, while whipping on medium-high.
When all the butter has been added, fold in the pineapple puree, rum, and coconut extract.
Pipe the buttercream on the cupcakes**, and garnish with a maraschino cherry, a pineapple chunk, and a parasol pick.