Method

• 1.
  Preheat the oven to 160°C fan-forced. Grease an 18cm x 28cm slice tin, at least 6cm deep, and line with baking paper. For the base, combine all the base ingredients in a bowl and mix well. Press into the prepared slice tin. Bake for 20 minutes, or until light golden. Remove from the oven and allow to cool in the tin on a baking rack.
• 2.
  For the marshmallow filling, place the sugar and 1/2 cup (125ml) water in a large, heavy-based saucepan. Put a candy thermometer in and turn on the heat. Without stirring, allow the sugar syrup to heat and boil until it reaches 120°C on the candy thermometer, then remove from the heat.
• 3.
  Meanwhile, place the warm water in a cup or bowl and add the gelatine powder, stirring to combine. Using a stand mixer fitted with the whisk attachment, whisk the egg whites to firm peaks.
• 4.
  Remove the sugar syrup from the heat at 120°C. Gently stir in the gelatine mixture until well combined. With the stand mixer on the highest speed, carefully pour the hot sugar syrup mixture into the egg whites. Add the vanilla, food colouring (if using) and puree. Continue to whisk for 5-10 minutes, or until the mixture thickens and increases in volume. It should appear pillowy while also remaining pourable.
• 5.
  Working quickly, pour the marshmallow over the cooked base. Cover the tin and place in the refrigerator for at least 1 hour, or until completely set.
• 6.
  For the topping, put the dark chocolate and coconut oil in a clean, dry, heatproof bowl over a saucepan of just-simmering water (the water should not touch the base of the bowl). Gently stir with a silicone spatula until melted.
• 7.
  Allow to cool slightly before spreading on top of the set marshmallow (you don’t want to melt the filling). Refrigerate to set again, around 15 minutes. Bring to room temperature before cutting into bars using a knife dipped in hot water.