You Are the Cindery Witch That Will Not Die.

Synopsis

I'm a magic apprentice. "My master," who has been living under this same run-down roof with me, is a shut-in girl who proclaimed herself to be a great witch. Despite sounding all high-and-mighty, my defenseless master loves to watch her disciple cooking for her. Our daily lives, filled with happiness, go by quietly. However, little did I know that behind that quiet, happy daily life is a terrible secret that involves the fate of the world... (Source: Kadokawa, translated)