Preheat the oven to 180°C and line two 18cm square sandwich tins with baking parchment.
Cream together butter and sugar, then beat in eggs one at a time.
Fold in the flour until smooth and divide the mixture evenly between the tins.
Bake for 18 to 20 minutes and verify they are cooked with a skewer.
Melt the white chocolate and spread it in a smooth layer onto a sheet of baking parchment.
Refrigerate the chocolate for 30 minutes until set firm.
Beat the icing butter with icing sugar and citrus zests until creamy.
Cut the set chocolate into twelve 11x7cm rectangles and trim the edges.
Sandwich the cooled cakes together with a third of the buttercream.
Spread the remaining buttercream over the top and sides of the cake.
Press the chocolate shards around the sides of the cake in an overlapping pattern.
Top with diced mango, toasted coconut, and additional lime zest to serve.