Preheat oven to 180C/350F. Line a 12-hole muffin pan with paper cases.
Peel, core and coarsely grate apple. Place apple in a small saucepan with dates, bi-carb soda and the water; bring to the boil. Remove from heat; cool for 20 minutes.
Beat butter, vanilla, sugar and egg in a small bowl with an electric mixer until light and fluffy. Stir in sifted flour and baking powder, then the cooled apple mixture. Spoon the mixture into cases.
Bake cakes for 15 minutes
Meanwhile, make coconut crust. Stir ingredients in a medium saucepan over medium heat until sugar dissolves.
Spoon hot coconut crust onto hot cakes; bake for a further 10 minutes or until crust is browned. Stand cakes in pan for 10 minutes; transfer, top-side-up, onto a wire rack to cool. Serve dusted with a little sifted icing sugar.