Specific to the area comprising the provinces of Milan, Varese and Como, should derive from nicknames originating from the archaic term Restello (park area, Quarantine Hostel), with reference perhaps to the locality of origin of the parent or to particular Hospitality characteristics of the same. Additions provided by Aldo Piglia, Milan could derive from the term dialectal restell ie rake (cf. Milanese-Italian Dictionary by Cletto Arrighi, Milan 1896). It would therefore be a derivation from the profession (peasant) of the ancestor. This hypothesis is reinforced by the distribution of this surname especially in the ex-rural areas.
You may be interested
Verba Volant, Scripta Manent