Reference for Challah 1:5

עִסָּה שֶׁתְּחִלָּתָהּ סֻפְגָּנִין וְסוֹפָהּ סֻפְגָּנִין, פְּטוּרָה מִן הַחַלָּה. תְּחִלָּתָהּ עִסָּה וְסוֹפָהּ סֻפְגָּנִין, תְּחִלָּתָהּ סֻפְגָּנִין וְסוֹפָהּ עִסָּה, חַיָּבִין בַּחַלָּה. וְכֵן הַקְּנוּבְקָאוֹת חַיָּבוֹת:

A batter whose start is spongy, and whose end is spongy, is exempt from <i>Challah</i>. Whose start is doughy and whose end is spongy, or whose start is spongy whose end is doughy, it is obligated in <i>Challah</i>. Similarly crumb loaves are obligated.

Jastrow