Franz Lehrndorfer (10 August 1928 – 10 January 2013) was a German organist and composer. A specialist in organ improvisation, he was for decades both the organist of the Munich cathedral Frauenkirche and the head of the department of Catholic Church Music at the Hochschule für Musik und Theater München.
You can hear him on Spotify.
He also includes improvisations on recordings of repertoire:
Celestial Christmas 5: Franz Lehrndorfer Plays Seasonal Music on the New Organ in the Dome at Munich
Includes a free improvisation on In dulci jubilo.
Includes a free improvisation on Sagt an, wer ist doch diese.