Melt butter at 70°C, 2 minutes at speed 2.
Add coconut, flour and brown sugar and mix 30 seconds speed 2 or until just combined. Put filling into a slice tin measuring approx 25 by 16 cm that has been lined with baking paper. Cook in a 180°C oven for 10 to 12 minutes.
Melt butter 80°C, 3 minutes at speed 2
Add the rest of ingredients for the caramel filling and cook 80°C, speed 3, 10 minutes.
Pour on top of base and bake for 10 to 15 minutes, until top is lightly set. Set aside to cool completly
Place the castor sugar, water and gelatine in main bowl and heat 90°C for 5 minutes at speed 2 until sugar has dissolved. Increse heat to 100°C and cook for a further 5 minutes at speed 2. Set timer for an hour and allow to cool.
Using egg whip beat for 20 minutes on speed 9 or until doubled in volume and stiff peaks form. Add vanilla and beat until well combined.
If using a stand mixer pour cooled marshmallow mixture into bowl and mix using the whip for approx 8 to 10 minute on the highest setting until doubled in volume and stiff peaks form, . Add vanilla and beat until well combined.
Spoon or pipe the marshmallow mixture over the caramel, spreading evenly. Place in fridge for 2-3 hours to set. Cut into squares to serve.