Preheat the oven to 140°C (fan forced); line the base of the tins with baking paper and grease well with butter.
Beat the butter and sugar till pale and creamy using an electric beater.
Pour in the melted chocolate and eggs; beat till combined and creamy.
Fold in the flour, almond meal, buttermilk and cocoa powder till well combined. The mixture is slightly thicker than regular cake batter.
Pour into tins and smooth the surface. Bake the medium tins for 35 minutes and the small one for 20 min or until a skewer inserted in the thickest part of the cake comes out clean.
Slightly cool before transferring onto a wire rack. Cool completely before applying the buttercream.