Make the cake layers: Preheat oven to 350 degrees. Grease pans and line with parchment. Sift together flour, baking powder, and salt. Whisk together egg whites and milk in a separate bowl.
Beat butter using the paddle attachment until soft and creamy. Add sugar gradually and beat until light and fluffy. Add the cream of coconut and mix until incorporated. Scrape down the bowl as needed. Beat in coconut extract.
Add flour mixture alternately with the egg white/milk mixture. Begin and end with flour mixture and beat until smooth on medium-low speed after each addition.
Divide batter between pans. Bake 6-inch cakes for 30 minutes or 8-inch cakes for about 35-40 minutes, or until a toothpick tester comes out clean. While the cakes are still hot in the pans, place a clean lint-free towel on top of the cakes and press gently to level them. Be careful because as you press this can cause steam to release. Fold the towel in half to double thickness; this will prevent burning your hand. Let cool slightly in pan, then turn out and cool completely. Torte each cake (cut in half horizontally) when completely cooled.
Make the buttercream: In an electric mixer fitted with the whisk attachment, mix together the butter and confectioners’ sugar on low speed. Gradually add the heavy cream until the mixture comes to spreading consistency. Add the rum extract and whip until light and fluffy. Remove half of the frosting and transfer it to a piping bag with no tip or coupler attached and cover the remaining frosting with a damp towel so it doesn’t dry out.
Assemble: Drain the pineapple chunks and pat them dry with a paper towel. Use the bottom of a glass to crush the chunks slightly and then pat dry again.
Pipe a small line of frosting around the top edge of one of the cake layers. Cover with a thin layer of rum frosting and scatter pineapple on top. Add another cake layer on top. Frost this layer but do not add pineapple. Top with a third cake layer, frost and add pineapple. The six-inch cake layers should go as follows:
Layer 1 – buttercream and pineapple
Layer 2 – buttercream
Layer 3 – buttercream and pineapple
Layer 4 – buttercream
Layer 5 – buttercream and pineapple
Layer 6 – top of cake, cover with buttercream
Apply a very thin layer of frosting on the outside of the entire cake (crumb coat) and then chill until firm.
You should have leftover rum buttercream in the piping bag. Save this for later use.
Meanwhile, make the blue curacao frosting.
Add 2 tablespoons blue curacao, the orange extract and the blue food color to the remaining frosting in the mixing bowl. Whip until well incorporated. Add additional confectioners’ sugar if the icing becomes too lax with these additions. Transfer the frosting to a piping bag with no coupler or tip attached.
When the cake is well-chilled, pipe blue frosting around the outside of the cake, about 2/3 of the way up. Continue the rest of the way up with the white rum frosting. Smooth the frosting with a spatula (don’t worry if the colors mix into each other – we want that to happen!). Use a bench scraper or cake smoother to even the buttercream on the sides of the cake. When you’re satisfied with the appearance, chill the cake until firm, about 30 minutes to 1 hour. To further smooth the frosting after chilling, use a spatula warmed in hot water (wipe dry first) to run over the surface of the frosting. This melts the butter in the buttercream and levels an uneven surface.
Drop a large open star decorator tip into a disposable piping bag and squeeze leftover rum buttercream into the bag. Pipe swirls of frosting on the top edge of the cake.
Garnish the cake with maraschino cherries and fresh pineapple slices. Store the cake in the refrigerator. Bring to room temperature before serving.