Remove crust from white bread and dice. Fry bread cubes in a pan with melted butter until golden brown.
Beat egg yolks in a saucepan with sugar until frothy. Add cream and slowly heat while stirring constantly. Warning: Egg yolk mixture must not cook!
Meanwhile, heat beer in a saucepan with cinnamon and lemon peel. After about 10 minutes, remove spices and carefully pour hot spiced beer, while stirring, into hot egg yolk-cream mixture. Remove the saucepan from the heat. Serve soup immediately in deep plates and garnish with croutons.