Step 1

Preheat oven to 180°C/160°C fan-forced. Grease a 6cm-deep, 22cm round cake pan. Line base and side with baking paper, allowing a 3cm overhang.

Step 2

Using an electric mixer, beat butter, sugar and vanilla until light and fluffy. Add eggs, 1 at a time, beating until combined. Stir in flours, cocoa powder, bicarbonate of soda, coffee powder, food colouring, water and milk. Pour mixture into prepared pan.

Step 3

Bake for 1 hour 15 minutes or until a skewer inserted in centre comes out clean (cover cake with foil if over-browning during cooking). Stand cake in pan for 10 minutes. Turn onto a wire rack to cool completely.

Step 4

Make the frosting: Place chocolate in a microwave-safe bowl. Microwave on medium (50%) for 3 to 4 minutes, stirring every 30 seconds with a metal spoon, or until melted. Cool for 10 minutes. Stir in sour cream.

Step 5

Cut cake into thirds horizontally. Place cake base on a plate. Spread one-quarter of the frosting over base. Top with cake layer. Spread one-third of remaining frosting over cake. Top with cake top. Spread remaining frosting over top and side of cake. Serve.