Hot plate for chocolate Dip-inator

The hot plate part for the Chocolate Dip-inator built by Hinge: http://www.thingiverse.com/thing:1832773
(Or is it Dyp-inator?)

A 12 V heating cartridge (the same type used in many hot-ends) is used to heat an aluminium disc (80 by 15 mm) to 50 degrees C. Since it is a low temperature application, the aluminium discs can be insulated with a slab of closed cell PE-foam packing material, but be aware, that even the modest hot end heating cartridge can easily send an insulated lump of aluminiu