Pre-heat oven to 150°C. Grease a round 23cm tin with removable base and line bottom with non-stick baking paper.
In a pot, simmer together water and 75g caster sugar. Remove from heat and stir in 180g of the chocolate and 150g butter until melted. Set aside.
Separately whisk the eggs and remaining caster sugar in an electric beater on high for 10 minutes.
Fold together the flour, chocolate mixture and egg mixture gently with a spoon until it is evenly mixed. Pour into tin and bake for 35-45 minutes or until a skewer comes out with the consistency of wet breadcrumbs. Set aside until cool.
Leaving the cake in its tin, push down until it is compact and flat.
Combine Tatua Chocolate Mousse, remaining sugar, chocolate and butter together in a pot over a low heat until melted and smooth.
Leave to cool then stir in scorched almonds and pour evenly onto cake base. Chill for 2 hours.
Heat tin over a hot element until cake edges begin to glisten. Slice with a hot dry knife while still chilled. Best served at room temperature. Garnish with extra Tatua Chocolate Mousse immediately prior to serving.