Step 1

Preheat oven to slow (150°C/130°C fan-forced). Grease two deep 20cm-round cake pans; line bases and sides with baking paper.

Step 2

Combine butter, white chocolate, sugar and milk in medium saucepan; stir over heat, without boiling, until smooth. Transfer mixture to large bowl; cool 15 minutes.

Step 3

Whisk sifted flours into white chocolate mixture then whisk in essence and egg; pour half of the mixture into one of the prepared pans. Whisk sifted cocoa into remaining mixture; pour into other prepared pan. Bake cakes, uncovered, about 50 minutes. Cool cakes in pans 5 minutes; turn cakes, top-side up, onto wire rack to cool.

Step 4

Combine milk chocolate and cream in medium saucepan; stir over low heat until smooth. Transfer to medium bowl. Cover; refrigerate, stirring occasionally, until chocolate mixture is of spreadable consistency. Reserve 1 cup of the chocolate mixture for spreading over cake.

Step 5

Split each cooled cake in half. Centre one layer of cake on serving plate; spread with ½ cup of the remaining milk chocolate mixture. Repeat layering, alternating colours. Cover top and sides of cake with reserved chocolate mixture.