Preheat the oven to 170 degrees Celsius (160 degrees fan forced).
In a large mixing bowl, whisk the egg whites and cream of tartar until soft peaks form. Slowly add the caster sugar a little at a time and whisk until stiff peaks are formed. Set aside.
In a separate mixing bowl, whisk the egg yolks with the additional caster sugar until a pale, thick and fluffy mixture is formed.
Add the coconut milk, vegetable oil, orange juice, zest, flour and baking powder and whisk until combined.
Gently fold the egg whites into the yolk mixture.
Pour into a 22cm Angel Cake tin (remember to not grease it. Poh also notes that you do not use a non-stick tin).
Bake for 50-55 minutes or until a skewer comes out clean.
When the cake is out of the oven, immediately invert the tin and leave the cake in the tin to cool completely on a flat surface (this takes approximately 2 hours).