Law and Order Criminal Intent episode “Death Roe”. Not only is the chef the killer, he has an incestuous relationship with his daughter, and ground up his victim and fed him to the employees.
Which reminds me that there was an L&O episode where a TV chef kills to try to keep his show from being canceled.
I’m getting the idea that “cooks who cook people” is actually the more popular option!
I considered that, but I thought it was too narrow - I guess I was wrong … maybe I’ll make the ‘project’ all cooks who cooked up people. 
Oooh, and The Cook, the Thief, His Wife and Her Lover, where the Lover, IIRC, is baked and force-fed by the Wife to the Cook.
Yeah, jolly film.
Damn, ninja’d, though I’m not sure who did the cooking. But I do recall that the wife made her husband eat some.
Mr Monk and the Foreign Man. Restaurant owner (who probably was a cook to start, if that’s not a stretch) kills someone while drunk driving and then murders a witness.
Also, the film Delicatessen. Mmm, cannibalism! Though it was post-apocalyptic, maybe that’s excusable.
Criminal Intent again - Salome in Manhattan. But I think it was the business partner (Shawn Hatosy, creepy as always) than was the murderer.
The Wife fed her Lover, who was cooked by the Cook, to her husband, the Thief, who had killed the Lover.
The Brewster Sisters in Arsenic and Old Lace often cooked a meal for their victims before giving them the poisoned wine.
The great Stanley Ellin’s great short story “The Specialty of the House” was made into a fifth-season episode of Alfred Hitchcock Presents, featuring the great Robert Morley.
I thought of Charly when I read the title but decided she really didn’t count as, even though she had crazy knife skills, she wasn’t a chef at all.
Mentioned above in #8, although evidently I got the title and author wrong.
Do restaurant owners count? If so, Eduardo/El Macho in** Despicable Me 2**. (I’m not sure if he actually killed anybody, but he sure tried.)
No, you were right. “Lamb to the Slaughter” is an iconic Roald Dahl story involving cook-murder, although the cook is a housewife. One of the best AH episodes. “The Specialty of the House” came later.
One of the finest Nero Wolfe mystery novels by Rex Stout is 1939’s TOO MANY COOKS. A famous chef is murdered by another famous chef at a famous chef contest.
No human flesh is consumed, though. Wolfe would have said “Pfui” to that.
Thought of her too. Real life example, though, whereas the OP just called for fictional portrayals.
Typhoid Mary never murdered anyone (except through idiocy).
In The Long Kiss Goodnight, the main character displays knife skills in the kitchen that are clearly a chef’s knife skills. While the director probably intended to show, simply, that she was good with a knife, there’s not much similarity between knife fighting and dicing an onion. So, from what we see, we must assume that she had spent some good hours working in a kitchen.
The cook kills the narrator’s mother in Life of Pi (embodied by the jackal and orangutan, respectively).
Recent Foreign language Oscar-nominee Wild Tales features a story about a restaurant cook who kills in an act of revenge.
We should continue evaluating Charley’s skill as this is one of my favorite movies ever and the more we speak of it, the better. I agree that her ability to dice onions and peppers has nothing to do with her ability to creatively kill with a butcher knife.
Well she also cusses like someone who worked in a kitchen. 
I could probably pull up a few more bits of evidence, but I’d have to watch the movie again… Welp, I guess I know what I’m doing tonight. 
…Eliot Spencer from Leverage.
And his most bad-ass moment (gloriously over-the-top) (Spoilers for Season 3)