First he found a piece of wood to turn into the board (this is very easy in our house), then he cut it into a circle. I didn't see how he did this because he was in and out of the workshop quicker than I could load an SD card into my camera, but drawing around a plate would be a good size.
Then he took an axe to a 2" wooden ball (literally) and chopped it in half to place in the middle of the board. If you don't have an axe handy (who does?) a good idea would be to cut the last inch or so from an IKEA rolling pin (the solid one piece type rather than the one with handles).