Found it! :) (And Heinrich spells it "jolli" which is why it was harder to find.) Copying for easy access:

Pro Fuer
Ecrit moi, du solst mir schreiben
Ce que tu fais, was du machst
Ce que tu dis, was du sachst
et tu doit etre jolli dans ta lettre,
und du solst erlich sein in deinem
brief, allor, je t'aimerai, So werde
ich dich lieb haben
Henri
Heinrich

Interestingly, he equates "joli" with "ehrlich" here, which I didn't expect! Hm.