Step 1

Preheat oven to 160C/140C fan forced. Grease a 22cm (base size) round cake pan. Line the base with baking paper.

Step 2

Combine the butter, caster sugar, brown sugar, chocolate and milk in a large saucepan. Cook, stirring, over low heat until just melted. Immediately remove from heat and stir until smooth. Set aside to cool until just warm.

Step 3

Add egg and whisk until combined. Sift the plain flour and self-raising flour over the cake mixture. Gently fold the flour into the cake mixture until just combined. Pour into the prepared pan.

Step 4

Bake for 1 hour 15 minutes or until the cake springs back when lightly touched in the centre. Set aside in the pan for 10 minutes to cool slightly before transferring to a wire rack to cool completely.

Step 5

To make the topping, place the chocolate and cream in a microwave-safe bowl. Microwave on High for 1 minute until chocolate has softened. Stir until smooth. Place in the fridge, stirring occasionally, for 2 hours until chilled and the mixture is spreadable.

Step 6

Spread the topping over the top of the cake to cover.