In Hilchos Challah Siman 329 Sif Beis the machaber paskens that if one made a dough to be cooked then it’s patur from challah. The Shach however argues and says that many poskim don’t hold like this and therefore one should be mafrish without a bracha. What about if someone had such a dough that they prepared, cooked, and never took Challah from and now it’s Shabbos. What should be done now? Can they be somach on the Machaber in such a case? Should they be mafrish with a katan? Can they be mafrish themselves even since maybe it’s only a chumrah?
Challah must not be taken on Shabbos, even where this is a stringency.
As poskim write, challah today is rabbinic, and therefore for matters of doubt one can be lenient, and where there is a need the cooked dough can be eaten on Shabbos. [This is true in spite of the fact that it is a davar she-yesh lo matirin after Shabbos.]
One should preferable leave some of the cooked dough for after Shabbos, as the ruling outside Israel where bread can be eaten on Shabbos, and some left for after Shabbos for purposes of challah.