This could be done with a normal ground plane by extending it out both sides of a board. A microwave transformer with the high voltage secondary cut out to make

This could be done with a normal ground plane by extending it out both sides of a board. A microwave transformer with the high voltage secondary cut out to make a 2 turn transformer could supply more than enough current... use a thermocouple the same way, and a Triac to control the primary, and Bob's your Uncle. Doing a row of vias on both sides then paralleling the top/bottom traces to make some big T shaped terminals might make it easier to get uniform current distribution.