Winter flower

A small yellow blossoming plant. I don't know the name, whether it is winter jasmine or winter aconite, or any other flower.
Excuse the bad quality, it was at a dark spot, and the plant was small (the blossoms just 1.5cm or so), and I had no lamp or tripod with me.
I just thought it funny to see fresh blossoms mid-winter, after some nights with temperatures of -6°C.
Thanks to BikerBear for hosting the Flower Friday challenge.