Melt the couverture in a water bath, not too warm. Mix with butter and about 50 g sugar until frothy. Add rum.
Beat the egg white with the remaining 100 g sugar.
Sift the flour, mix with the almonds and cinnamon.
Stir some of the beaten egg white into the butter mixture. Then fold this soft mass into the stiffly beaten egg white with a wooden spoon. Carefully fold in the sifted flour as well.
Line the loaf tin with parchment paper and carefully pour in the chocolate dough.
Bake at 170 ° C for about 45 minutes. Dust with icing sugar after cooling.