Preheat oven to 180 C / Gas 4. Grease a baking dish.
Mix rice flour, caster sugar, cocoa powder, brown sugar, salt and baking powder together in a large bowl; add coconut milk, apple sauce, coconut and coconut oil. Blend the mixture until it thickens; pour into the prepared baking dish.
Bake in the preheated oven until the top is dry and the edges have started to pull away from the sides of the pan, about 30 minutes. Cool about 10 minutes before cutting into squares.