For chocolate malt ice-cream, stir chocolate and half the cream in a small saucepan over low heat until melted and smooth (2-3 minutes). Set aside. Whisk remaining cream, milk and malt powder in a saucepan over medium heat and bring to just below the boil. Meanwhile, whisk yolks and sugar in a bowl until pale and fluffy (3-4 minutes). Add hot milk mixture in a thin steady stream, whisking continuously until incorporated, then pour custard into a clean pan and stir continuously over low heat until mixture thickly coats the back of a wooden spoon (4-5 minutes). Remove from heat, add chocolate mixture, whisk to incorporate, then strain into a bowl placed over a bowl of ice and stir occasionally until cool. Refrigerate until chilled, then churn in an ice-cream machine and freeze until required. Makes about 1.2 litres.
Preheat oven to 170C. Beat butter and 250gm sugar in an electric mixer until pale and fluffy (2-3 minutes). Scrape down sides of bowl, add eggs and beat to incorporate. Sift in flour, 60gm cocoa and baking powder, stir to combine, then stir in milk, 60ml stout and chocolate. Divide among six 350ml ovenproof ramekins or bowls. Combine remaining sugar and cocoa in a bowl, add 330ml boiling water and remaining stout, stir to combine, then carefully pour over puddings and bake until risen and puddings spring back when lightly touched (30-35 minutes). Dust with cocoa and serve hot with chocolate malt ice-cream.