Traditional French Breadboard

On a recent trip to England I was taken to a very Parisian style café. Hanging on the wall were several exquisite large bread boards of varying shapes.
You’ve probably seen them – 45cm in diameter with a narrow handle. They fascinated me, how could something so wide and thin not be warped?
As luck would have it, my sister has a couple tucked on a high shelf in her kitchen. It wasn’t until I had the chance to take them down and give them a good assessment that the warp-free secret was revealed.