To make the okonomiyaki sauce, add ketchup, Worcestershire sauce, soy sauce and sugar to a small saucepan over low heat until the sugar is dissolved and the mix. You can drizzle this over the pancake straight from the pan or transfer it to a squeeze bottle when it has cooled down.
To make the okonomiyaki, you'll need a non-stick, deep-sided 9-inch (23 cm) frying pan and a plate that fits snugly on top of the pan to turn the pancake over.
In a large bowl add the sliced cabbage, green shallots, yamaimo (if using) and beaten eggs. Add the dashi stock (or water) then the flour and combine well. The mix should be wet and a little sticky.
Heat the frying pan to medium high and add the mixture, spreading it out in one thick layer.
After a couple of minutes, check the doneness of the bottom of the pancake using a fish slice (thin slotted metal spatula).
When the bottom is golden brown, have the plate ready to flip the pancake on to. Check that the pancake is not stuck to the pan by shaking the pan back and forth.
With the plate over the top of the frying pan, swiftly flip the pan onto the plate and the pancake should be covering the plate.
Place the frying pan back on the heat and gently slide the pancake back into the pan. Cook until the underside is golden and transfer to a serving plate.
Pour the okonomiyaki sauce in a zig-zag pattern over the top of the pancake. Turn the plate 90° and do the same with the mayonnaise. Sprinkle on sliced spring onions, dried seaweed, furikake, and bonito flakes. Serve immediately.