This will need a microcontroller to read and report the temperature.  There are several ways the temperature could be reported, locally or remotely.  The simplest would be to write it on a display connected locally, but it would be more useful if the temperature could be transmitted and displayed remotely so you can check up on it from a distance.  A development board with a wireless radio can do both.  If I decide to take this to production, I would like to include a long range radio that can go through walls so that you can keep tabs on a smoker from inside your house.  A sub-GHz radio like Z-wave used in home automation would be ideal, but the development boards are a little steep for a hobby project, so I think I'll stick with BLE.  There is no problem finding a low cost BLE development board, the difficulty is choosing from the myriad of options.  The ideal board for this project would include BLE and a low power display with easy to use tools.  After checking a few of my favorite hobby sites, I found just the board at Adafruit under Wireless/Bluetooth.  The Pixl.js board includes both BLE and a display, and it is programmed in Javascript with tools that run in the browser.  I can even program it using my chromebook.  It doesn't get much easier than that.  It is not the lowest priced BLE option, but the included display will save me from having to by it separately.  They also have a Puck.js if I want to have a headless sensor to broadcast to a remote display.