See also pesturie, which is synonymous but derives from a different etymological root. Alternatively, the -ur ending could also be interpreted as an agent suffix, which would make the word a variant spelling of the equally rare pestrer2.
s.
1kneading (into a paste or dough):
(
MS: s.xiii/xiv
)
ut arte pincendi (glosses: (L) de pestrur)(var. (C: s.xiii2) de peyster; (D: s.xiii/xiv) pester) in usu panis transformari possit
i 187.162 and ii 78.162
pestrur (s.xiii/xiv)