Mariticide: Unnatural Causes - Home Cooking (1986). This was the first movie I remember seeing (at age 4-7 or something) that featured a mariticide - at that young age I couldn't get my head around why someone would murder their husband (or wife) - it was especially memorable to me for some reason (locking the husband in a sauna, then drowing out his screams for help with food processors etc). The episode on YouTube
here. Stared Brian Cox as the husband, and Prunella Scales as the wife. I asked on
r/tipofmytongue to get the
answer of which movie I was thinking of.