In a saucepan, combine the milk and sugar and whisk together. Gradually add the semolina, then the egg, whisking constantly. This way, the milk doesn't get too hot and the egg cooks slowly without forming lumps in the pudding.

Add the mashed banana and cocoa powder, and continue stirring. Near the end, add the vanilla and cardamom.

When the pudding starts to thicken, add the butter and mix well.