Preheat oven to 180 degrees C and line a 9"x9" square brownie tin with tinfoil
Base
Melt butter and brown sugar in a medium sized pot until sugar has dissolved. Stir in flour, baking powder and coconut and combine.
Press into prepared tin and press down with the back of the spoon. Bake for 10 minutes until starting to go brown around the edges.
Filling
While base is baking, combine all ingredients in a pot and cook over a medium heat for 5 -10 minutes until the mixture almost comes to the boil. Stir continuously so that it doesn't burn on the bottom.
Remove the base from the oven and pour the filling over top, tilting the tin so that the filling covers the whole base.
Bake for 8 minutes until the filling is golden brown on top. Remove from the oven and allow to cool.
Topping
Melt chocolate and butter in a heatproof bowl either over a pot of boiling water on the stove or in the microwave. Once the slice is cool, spread the chocolate topping over and allow it to set.
Cut into squares and store in an airtight container for 1-2 weeks.