Lauda Sion (Ecce Panis) Opus 45, No. 7 from Dupre's Eight Short Preludes on Gregorian Themes.
The registration calls for 8, 4 and Mixtures. I turned on all the Mixtures on the Klais organ (6 in all!), coupling all three manuals together. Yes, it isn't the best for counterpoint music, but it gives such a wonderful sound!