The Posha and the Thermomix TM7 are the closest things to a home robot chef that mere mortals can afford. The catch is that you’re the prep cook.

The holiday is still almost a week away, and I'm sick of Thanksgiving. I've already made four rounds of mashed potatoes, three of mac and cheese, and three turkeys (with more still waiting in my fridge) as part of testing smart probes to help smoke turkeys outside and preparing seven-course holiday meal kits for friends and family.

I was eager to finally outsource some of the cooking by testing two very different robo-chef devices, the Thermomix TM7 and the Posha kitchen robot. Both promise to plan my meals and also do most of the cooking, which sounds pretty good to me.

The Thermomix descends from a German device launched in 1968—a time when the best-known robot chef was cartoon Rosie on The Jetsons—that was essentially a blender with a heater. It's since caught on big in countries from Italy to Portugal ...