Grease and flour a 25cm loaf tin and preheat oven to 180°C.
Mix the dark ale and cocoa powder into a smooth paste.
Beat the butter and brown sugar until creamy and incorporate eggs one at a time.
Stir in the cocoa mixture and sift in the flour, baking powder, and bicarbonate of soda.
Pour batter into the tin and bake for 30-35 minutes before cooling on a rack.
Melt the dark chocolate in a bowl over simmering water.
Beat icing sugar and butter, add 60ml of ale, and fold in the melted chocolate.
Whisk double cream, muscovado sugar, malt extract, and salt until thick and smooth.
Slice the completely cooled cake into portions.
Spread icing over the cake and serve with a dollop of malt cream.