Grease a 2-litre (8-cup) pudding steamer; line base with baking paper.

Stir chocolate and butter in a medium saucepan over low heat until smooth. Remove from heat; cool for 10 minutes. Stir egg yolks and extract into mixture, then ground almonds and sifted flour.

Beat egg whites in a small bowl with an electric mixer until soft peaks form. Add sugar; beat until sugar dissolves. Fold egg white mixture into chocolate mixture, in two batches. Spoon mixture into pudding steamer.

Place steamer, without lid, in a 4.5-litre (18-cup) slow cooker with enough boiling water to come halfway up side of steamer. Cook, covered, on high, for 2 hours or until firm.

Remove cake from cooker. Immediately turn onto a baking-paper-covered wire rack; cool completely.

To make caramel icing, melt butter in a small saucepan over medium heat. Add brown sugar and milk; cook, stirring, over medium heat until sugar dissolves. Bring to the boil. Reduce heat; simmer for 1 minute. Remove from heat. Whisk in sifted icing sugar until smooth.

Pour icing over cake before serving.