Preheat fan-forced oven to 120°C/250°F and line 2 trays with baking paper
In the bowl of a stand mixer, whisk the egg whites and cream of tartar on medium-high until stiff
Gradually add the caster sugar, 1 tablespoon at a time. Whisk each spoonful for 30 seconds (set a timer!)
Once all of the sugar has been added, continue to whisk until mixture is thick and glossy -about another 6-7 minutes
Combine and sift the cocoa and icing sugar, then gently fold it through the meringue mixture (doesn't need to be completely combined)
Using an ice cream scoop, mound 2 scoops of mixture onto tray and press down slightly to make a divot in the centre of each. Place 5 giant meringues per tray
Melt the chocolate in a microwave and allow to cool a little, before swirling through the meringue.
Dollop a teaspoon of melted chocolate onto each mound, then swirl through with a toothpick or skewer.
Place the trays into the oven and bake for 1 hour. After 1 hour, turn the oven off and allow the meringues to cool in the oven without opening the oven door
Serve when cool, or place in an airtight container for up to 3 days