T he only people who really know what it’s like to work behind the scenes on a powerhouse program like Saturday Night Live ...

The “Bottoms” star plays an aspiring stand-up comic and au pair contending with the disappearance of a teenage girl she used to nanny.

Anyone who has seen “Bottoms” or “Shiva Baby” knows Rachel Sennott is irreverent, witty, and laugh-out-loud funny. And thanks to HBO, she’ll soon be front and center on her own series.

But she plays a supporting role in the film; the lead belongs to Rachel Sennott, making her feature film debut. (Sennott had another movie at festivals before Shiva, but it didn’t make it to ...