Cascade PID temp controller, chocolate tempering

[Riskplan]

I'm building a simple DIY chocolate tempering machine. The heat source is rough service light bulbs in an outer air chamber surrounding a bowl that spins . I have it currently wired to 1 PID controller. the problem I'm having is either proper tuning of the one PID controller, or a need for a second loop controlling the air temperature in the chamber due to lag between heat source and actual chocolate temp. I can't seem to find any information on how to wire a cascading PID arrangement with a second PID. I have seen some expensive two loop controllers. Are there specific inexpensive controllers that work for this task? I don't see any of the lower-cost controllers having a way to control a set point as an input from another controller.

 

[Harald Kapp]

Do you need a PID controller for this? What are the accuracy requirements? Maybe +-2 °C? As the main thermal inertia is within the chocolate itself, wouldn't a simple bang-bang controller suffice?