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Chocolate and buttermilk slab cake

Buttermilk is the bakers' secret weapon here, adding a subtle tang to the sweet frosting and contributing to an ultra-tender crumb in the cake itself. Try it for yourself and see.

By Emma Knowles
  • 20 mins preparation
  • 50 mins cooking plus cooling
  • Serves 8 - 10
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This lush cake is a super-simple melt-and-mix number. Buttermilk plays a role in both the batter, where it creates an ultra-tender crumb, and in the frosting, where it cuts the sweetness. This cake is just as good a few days after baking, but you'll be hard-pressed to resist it for that long.


  • 280 gm caster sugar
  • 120 gm dark chocolate (54%-58% cocoa solids), finely chopped
  • 90 gm butter, diced
  • 225 gm (1½ cups) plain flour
  • 1½ tbsp Dutch-process cocoa, sifted
  • ¾ tsp bicarbonate of soda
  • 110 ml buttermilk
  • 1 egg, plus 1 egg yolk
  • Freeze-dried raspberries (optional; see note), to serve
Chocolate-buttermilk frosting
  • 150 gm dark chocolate (54%-58% cocoa solids)
  • 100 gm softened butter
  • 120 gm (¾ cup) pure icing sugar
  • 70 ml well-shaken buttermilk


  • 1
    Preheat oven to 160°C. Butter a 15cm x 30cm rectangular cake tin and line it with baking paper. Combine sugar, chocolate, butter and 180ml water in a large saucepan and stir occasionally over low heat until melted and smooth. Remove from heat, cool slightly, then sift in dry ingredients and whisk until smooth. Whisk in buttermilk, egg and yolk until smooth, pour into tin and bake until centre springs back when slightly pressed (45-50 minutes). Cool in tin.
  • 2
    For chocolate-buttermilk frosting, melt chocolate in a bowl over a saucepan of barely simmering water, stirring occasionally, until smooth. Cool to lukewarm, then transfer to an electric mixer, add butter and beat until fluffy (5-6 minutes). Beat in icing sugar and buttermilk until smooth, then spread onto cooled cake and serve scattered with crumbled freeze-dried raspberries.
  • undefined: Emma Knowles