Preheat oven to 350 degrees. Grease and flour 3 tall 6″ cake pans. (Use your coconut flour). OR Prepare muffins tins enough for 24 cupcakes.
Whisk together the cake flour, coconut flour, coconut milk powder, baking powder, and salt. Set aside.
Beat together the coconut milk, vanilla, and eggs whites. Set aside.
In a large bowl, beat the butter and the sugars until light a fluffy. Scrape down the sides and bottom of the mixing bowl. Beat for at least 3 minutes more.
Add 1/4 of the flour mixture. Mix until combined, and scrape the bowl.
Add 1/3 of the milk mixture, and mix until combined. Alternate adding the flour and milk mixtures, ending with the flour mixture.
Scrape the sides and bottom of the mixing bowl. Beat for 1 more minute.
Divide the batter between the three cake pans – or – the muffin tins.
Bake 30-35 minutes, or until the cakes are lightly golden and springs back to the touch. The toothpick test should come out clean.
Remove from oven and place on a rack to cool for about 10 minutes. Turn out the cakes – or – removed the cupcakes from the pan. Return to cooling rack until completely cool.
Put the coconut flakes into a small bowl. Be certain to remove clumps.
Add the cream of coconut and the rum. Stir the mixture until the coconut is completely covered. Set aside until ready to prepare the cakes.
In a large mixing bowl, beat the butter until fluffy and light in color. Be certain to scrape the sides occasionally.
Add the whipping cream. Continue beating for 2-3 minutes.
Add the powdered sugar, 1/2 cup at a time. Beat thoroughly between additions, and scrape sides of the bowl.
Add the rum. Beat thoroughly. If the buttercream is too thin at this point, add 1/4 more powdered sugar at a time until it reaches your desired consistency.
Assembly of Cake
Cut each of the layers in half so that you have four cake layers.
Place a dollop of buttercream on your cake tray. Place the first layer of the cake.
Put a semi-thin layer of buttercream on the top of the cake. (You’ll do the sides in just a minute.) Pipe a rim of frosting around the outer edge of the top. (think of it as a bumper ring)
Spread the Coco-Rum Filling inside the ring of buttercream.
Place the second layer of cake. Repeat steps 3 and 4 for the next two layers. Place the final layer of cake. Stabilize with cake picks, if desired.
Spread a thin layer of buttercream on the top and sides of the cake. Place in the freezer for 5 minutes. (This is your crumb layer and will help keep the final frosting layer look pretty and crumb-free)
Now, spread the rest of your buttercream on the top and side of the cake. Pipe ruffles, frost in swirls… basically however you would like your cake to look.
Sprinkle with coconut flakes and any remaining coco-rum filling.
Assembly of Cupcakes
Core the center of each cupcake.
Spoon the Coco-Rum Filling into the cupcake center. Just to the top of the hole.
Spread a thin layer of the Rum Buttercream, start from the center and work towards the edge. Free for 5 minutes.
Pipe the remaining buttercream onto the cupcake, as desired. Top with coconut flakes, if desired.