Reduce the balsamic vinegar with the rosemary by half. Remove the rosemary, season the sauce with salt and pepper.
Brush the meat with mustard, season with salt and pepper. First fry it vigorously in the clarified butter, then continue frying on a lower level if desired (e.g. medium).
Stir the 40g butter into the sauce, do not let it boil anymore.
Arrange everything together.
Potato gratin and broccoli go very well with this.