How would *I* do it? An 8-pin microcontroller, two resistors and
that's about it (plus power supply, two thermistors and the adjust
pot), assuming it was for more than just one piece to make writing the
code worthwhile.

You might find it easier to start with linear temperature sensors such
as LM50s (500mV +10mV/°C output) and use some op-amps to get the
effect you want. Then it's just op-amps 101 and pretty easy.

Many thanks for the pointer. I didnt realise that there was a linear temp
sensor such as the LM50. Last time I was involved in a temprature project
the choice was thermistors or thermocouples! Definatly looks like a easier
way to to than thermistors.