"Obelias bread is so named either because it is sold for an obol, as in Alexandria, or because it used to be baked on spits (obeliskoi)" (Athenaeus, Deipnosophists 111B). The first of these meanings ought really to produce obOlias, and sometimes it does (see LSJ s.v., web address 1); but as Athenaeus shows, not necessarily. Nevertheless, the "spit" connection is the authentic one (cf. omicron 6).
cf. Pausanias the Atticist, Moeris the Atticist, Hesychius, Photius, ps.-Zonaras.