Johann Christoph Kellner (1736-1803), Fantasia in G moll. Sheet music can be found in Incognita Organo Volume 18, editor Ewald Kooiman. More pieces of Kellner can be found in my playlist: https://www.youtube.com/playlist?list=PLNFZTCpjQ59UConkh9qnDbG-RFU7cGio3. Played on Sonarte organ with Hauptwerk, Mascioni, Giubiasco, Switzerland