Wikipedia
Valse-Impromptu, S.213, is a waltz for solo piano composed by Franz Liszt in the key of A-flat major.
The date of composition for the piece is not clear; however it appears to have been composed in the years between 1842, and 1852, the year in which it was published. This is the version commonly heard today; however, there exists another version (c.1880, S.213a) described as "Valse-Impromptu with later additions". This longer edition was recently recorded for the first time by Australian pianist Leslie Howard as part of his complete recordings of Liszt's piano works. Performances of the Valse last approximately 5 minutes 30 seconds, depending of course on the pianist. The extended version lasts about 1.30 minute longer.
Despite being arguably one of Liszt's lesser known pieces Valse-Impromptu has been recorded by such illustrious pianists as Josef Hofmann, Georges Cziffra (DVD), and Jorge Bolet, and frequently appears in collections of piano works by the composer.