It is either a movie or an episode of a TV show, where a grandmother dies and the main character recieves a bread starter as an inheritance. The bread is seen as a family heirloom and I believe the character might throw it out and either struggles to remember the recipe or another character still had a duplicate of the bread starter.
“True Blood” maybe.
“Brooklyn Nine-Nine”? https://brooklyn99.fandom.com/wiki/Chasing_Amy
In “Atypical” (s4e4), there is something like that when Chuck’s sourdough is thrown away.
https://atypical.fandom.com/wiki/Starters_and_Endings