There are a few recipes in Wiener for beef broth with various egg-based additions, and they all sound good. One has to start somewhere, so I did the version with crepes (Flädli here).
For the broth: 500g beef (siedfleisch), one leek, one carrot, one onion (with peel), half a celery root, a bit of cabbage, one bay leaf, a few peppercorns, 1.5l water. Bring to a gentle simmer and let cook, uncovered, 2 hours. Strain, let cool overnight, remove the fat layer, strain through cheesecloth, reheat and adjust salt.
For the crepes: 2 eggs, 250ml milk, 100g flour, 1/2 package chives (cut into 1/2 cm lengths), a big pinch of salt. Cook the crepes with clarified butter and then let them cool.
To serve: put some very finely diced (brunoise) carrot and pfaelzer in the bowls, heat the bowls, roll the crepes and slice them crosswise into threads (chiffonade), finally add the broth.
We ate this quite good soup with some roasted cauliflower and escarole with creme fraiche.