Step 1

Preheat oven to 180°C. Grease two deep 20cm round cake pans; line bases with baking paper.

Step 2

Beat butter, extract and sugar in a large bowl with an electric mixer until light and fluffy. Beat in egg yolks, one at a time, until just combined. Stir in sifted dry ingredients and buttermilk.

Step 3

Beat egg whites in a clean large bowl with an electric mixer until soft peaks form; fold into cake mixture, in two batches. Divide mixture into pans.

Step 4

Bake cakes 1 hour or until a skewer inserted into the centre comes out clean. Cool cakes in pans.

Step 5

Make chocolate icing; reserve half the icing to cover top and side of cake.

Step 6

Split cakes into three layers; place one layer on a plate, spread with one-fifth of the icing. Repeat layering with cake and icing, finishing with a cake layer. Spread reserved icing over top and side.

Step 7

Whisk chocolate and butter together in a medium bowl; whisk in sifted icing sugar. Cool icing to room temperature; whisk until thickened and spreadable.