Step 1

Preheat oven to 140°C (120°C fan forced). Grease two x 20cm (8-inch) round cake pans. Line base and sides with baking paper, extending paper 5cm (2 inches) above sides.

Step 2

Stir chocolate, sifted cocoa and the water in medium saucepan over low heat until smooth. Transfer mixture to large bowl, cool 15 minutes.

Step 3

Add butter, sugar, eggs, extract, sour cream and sifted dry ingredients to chocolate mixture, beat on low speed with electric mixer until combined. Increase speed to medium, beat about 3 minutes or until mixture is smooth and changed to a paler colour.

Step 4

Spread mixture into pans, bake about 1¼ hours. Stand cakes in pans 5 minutes, turn, top-side up, onto wire racks to cool.

Step 5

Meanwhile, make milk chocolate ganache. Combine ingredients in large heatproof bowl over large saucepan of simmering water, stir until smooth. Cover, refrigerate about 3 hours or until thick. Beat ganache in large bowl with electric mixer until firm peaks form.

Step 6

Split cakes in half, sandwich cakes using about ½ cup of the ganache between each layer. Position cake on cake board, secure with a little ganache. Spread cake all over with remaining ganache. Position candles on cake.