Preheat oven to 180°C and line a 22cm square cake tin with baking paper.
Combine butter, chocolate, cocoa powder and water in a medium size saucepan over medium heat. Cook, stirring until butter is melted and the mixture is smooth. Add egg yolks, sugar and almond meal to the chocolate mixture.
Using a stand mixer fitted with the whisk attachment, beat the egg whites on medium speed until soft peaks form. Add half the egg whites to the chocolate mixture and fold in gently to combine. Then add the remaining egg whites, gently folding to combine.
Pour the cake mixture into the prepared cake tin and bake for 45-50 minutes or until a skewer inserted into the middle of the cake comes out clean. Allow the cake to completely cool before cutting into squares and serving. Note: the cake will appear quite wet until it's cool.