Dan Ternes blogged about his Arduino-based controller for analog slow cookers:
With the AC power control figured out, I considered the User Interface. I opted for something simple. The Adafruit RGB LCD Shield would work well as it had both a display and buttons built in. Sure, I could have beat this project about the head and neck with “IoT”-this and “ESP8266″-that, but I was feeling lazy and just wanted a simple timer control. Of course, there’s nothing that says I won’t add some kind of wireless connectivity, but for now, local control is fine.
Code is available on github.
More details at Maniacal Labs project page.