Mix all the batter ingredients in a large bowl using an electric whisk with dough hooks until smooth.
Divide the batter equally between two medium-sized heatproof bowls and a small springform pan. Bake for 60 minutes in a preheated convection oven at 360°F. Let them cool for one hour.
Turn one of the cakes out of its bowl onto your work surface. Level the large flat side with a sharp knife. Repeat with the second cake and the cake from the springform pan.
Turn the first dome cut side up and spread a layer of chocolate buttercream on top. Place the cake from the springform pan on top and cover with chocolate buttercream. Place the second dome cut side down on top.
Cut a depression in the top of the cake and hollow it out with a spoon. Flatten the rim, leaving an edge about half an inch wide.
Cover the hollow and edge with white buttercream. Cover the outside of the cake with chocolate buttercream, except the top.
Sprinkle roasted coconut shavings over the entire cake, except the top.
Mix pineapple juice and coconut milk until frothy. Add whipped cream stabilizer if needed. Pour the cream into the hollow of the cake.
Decorate with a cocktail umbrella, pineapple slices on a skewer, and a colorful straw.