Confined to the fortress of Hohenasperg from 1777 to 1787, Schubart spent his time writing and composing. The Musicalische Rhapsodien is a collection of his own vocal and keyboard music, all three parts of which are prefaced with writings in Schubart’s idiosyncratic style. In a letter to his son dated 12 May 1786, Schubart wrote “Das zweite Heft der Rhapsodieen ist gut ausgefallen. Zum 3ten schik ich ein paar neue Lieder und Klavierrezepte” (Schubart 1849, ii.241-42). The sixth of the seven “Klavierrezepte” features recommendations of composers worthy of study, while still insisting on the importance of individual creativity and originality. Apart from “Mozart, the shimmering (one)”, the passage refers to:

?C. P. E. Bach (1714–1787), “with all his deep individuality”
Johann Gottfried Eckard (1735–1809), “the richly melodious man”
Leopold Kozeluch (1747–1818), “the glorious”
Muzio Clementi (1752–1832), “the original”
Franz Ignaz von Beecke (1733–1803), “the tone painter” (and dedicatee of the volume)
Joseph Haydn (1732–1809), “the bold temperamental (one)”
Ernst Wilhelm Wolf (1735–1792), “the correct”
Georg Joseph Vogler (1749–1814), “the strong”

Another edition of this passage (quoted in Neue Folge, 109-110) is almost identical, except that Mozart is there called "den Genialischen" (the congenial one).