Heat the beer and sugar. Pour in the whisked milk with the cornstarch. Season with one or two cloves, a little cinnamon, the grated zest of a whole lemon and the juice of half a lemon and a pinch of salt. Bring everything to the boil, stirring constantly. Remove from the fire and bind with the two egg yolks that you have mixed well with the rum. Serve the soup with toasted white bread rolls.