I'm still not sure about this cut of beef, it only said "Irish baby top" (600 gram) and google isn't very helpful to understand what the dutch equivalent is. These were my google-results: runderkogel, biefstuk van de baby -top (de rosbief uit de achterbil), Babytop (Kogel van de bovenbil).
So I decided to treat it as "rosbief", vacuum-packed it with two tablespoon of duck fat, 1 clove of garlic and a few sprigs of thyme. (toffee-wrapped in some cling foil). Salt and pepper directly on the meat. Then cooked it at 50C for 65 minutes. Then pat-dried and pan-fried it in 4 minutes until all sides were nice and brown, rested it for a couple of minutes, then carved it.
It was nice and tender, perfectly pink. Taste wise I wasn't 100% happy, it had a tiny, little, funny taste. Maybe butter would have been better than duck fat. And a bit of horseradish sauce on the side.
But I'm happy with the result anyway. Better than last time, when I tried to cook a piece of "rosbief" for 7 hours at 55C and it turned out to "well-done" for my taste. I like rare and pink meat.
Update: the next day it was nice too: Thinly sliced on a sandwich with horseradish cream .