Okonomiyaki is getting slowly more popular outside of Japan. It’s often described as a Japanese pizza, but it’s more like a savory pancake.
Okonomiyaki was invented, they say, in Osaka, which is a city famous for cheap and good eats. Okonomiyaki is a snack more than a full meal, though it is pretty filling. It’s a quintessential yatai or streetside food stand food, though nowadays you’re more likely to eat it indoors than sitting at an outside stall. It’s a very communal type of food, especially if you cook it on a tabletop griddle.
This is a fairly authentic recipe I think, or as authentic as a Tokyo born-and-bred girl can get.
Okonomiyaki uses some very Japanese ingredients which may need some explanation. (Check out the ever growing reader-contributed list of Japanese grocery stores  to find these ingredients.)
Nagaimo is a starchy root vegetable, which can be known under the names taro root or under that annoying generic term for any starchy root vegetable unfamiliar to to the Westerner, yam. It is usually sold in cut up lengths wrapped in plastic. It looks like this:
You will use this grated into a gooey, sticky pulp, which looks like this. (This is where some juvenile surfer discovers this page and snarks about how it looks like spit, sperm, or a combination of both.)
A lot of people have a mild allergic reaction to raw grated nagaimo. I have that reaction - it makes me itch a bit. So I avoid skin contact with the raw surface by only peeling as much of the root as I need (for this recipe, about 4 inches or 10 cm) and holding the root in its plastic wrap while grating. To keep the rest of the root, let the exposed cut end dry off a bit then wrap securely in plastic.
The glutinous, gelationous quality of the nagaimo gives the okonomiyaki batter a certain bounce. I’ve tried substituting grated potato , which sort of works, but nagaimo is better. The only subsitutes for nagaimo are even harder to get outside of Japan, yamaimo or yamatoimo. I can get raw nagaimo in my tiny local Japanese grocery, so any decent Japanese grocery store  should have it.
There is a dried yamaimo powder which can be used instead. (In practice though, I’ve found that if a store has dried yamaimo powder, it’s also likely to have the raw nagaimo root too, and I prefer to use the latter. If you can only get stuff by mailorder though, the powder is more handy. Japan Centre  carries it.)
This is a dried, very green version of nori seaweed. It’s usually sold in finely shredded almost-powder form. It’s quite inexpensive, so it’s worth buying. A substitute would be finely shredded regular nori, but aonori is usually a bit cheaper. Used as a topping.
Dried bonito flakes. One of the essential Japanese ingredients . Used as a topping with aonori.
This is a sweet version of tonkatsu sauce, which is described here . This is available at Japanese grocery stores. You can use tonkatsu sauce instead. It’s not essential to use this sauce - my mother for instance prefers a little drizzle of soy sauce on her okonomiyaki instead.
Mayonnaise is used as the sauce on top of the okonomiyaki by a lot of people, though it does make the whole thing very rich. A Japanese brand like Kewpie is preferred, though Hellman’s or whatever works too. It adds richness and a touch of acidity.
The base of Japanese food! Here is the basic recipe , but you can use a pinch of dashi stock granules (such as hondashi).
Pickled and red dyed ginger. Colorful, cheap, and cheerful. Available at any Japanese grocery store.
Tenkasu is little bits of batter that fall into the oil when you are frying tempura. It’s used as a flavoring ingredient in a surprising number of dishes. You can actually buy premade tenkasu in a well stocked Japanese grocery store, but I find it hard to justifying spending money for something which is just oily bits of batter. On the other hand, I don’t really make tempura often enough to have a stock of tenkasu around. So what I do is to make some of the okonomiyaki batter into impromptu tenkasu. I’ll show you how in the instructions.
Tiny dried shimp. This is an optional but nice ingredient to put in.
This is the part of pork that gets turned into bacon. In Japan you can get this part very thinly sliced, as a normal supermarket cut (butabaraniku usugiri). Elsewhere, you may have to ask your butcher to slice it for you. If you can’t get it pre-sliced, get a chunk of pork belly, freeze it until it’s quite stiff but not a solid ice block, and slice it yourself.
You should have these around. Regular flour is fine - you only need a little bit of it as a binder.
Professional okonomiyaki stores may use beautifully finely shredded cabbage, but if your knife skills do not measure up, roughly chopping it (even in a food processor) is fine.
So, if you’ve managed to get all the ingredients together, let’s make okonomiyaki.
This makes 3 medium or 2 big okonomiyaki. A medium okonomiyaki would feed one person. A big appetite can handle one big okonomiyaki. You can also cut them into slices to serve many as appetizers or beer snacks. Increase the amounts proportionately for more servings.
Peel and grate the nagaimo, following the hints above for protecting your hands. Mix with the dashi and flour, and add two of the eggs. It should be a rather loose batter.
At this point, if you don’t have any tenkasu on hand, heat up some oil in a small frying pan. Dribble some of the batter in the hot oil.
Cook until golden brown. Drain off the oil (you can use it to cook the okonomiyaki) and allow the tenkasu to cool.
Add the chopped cabbage to the batter.
Add the other egg. Stir with a big spoon or a spatula to combine.
Add the other ingredients except the pork. Crumble the tenkasu with your hands a bit before adding. Stir to combine.
Heat up your griddle pan or big frying pan. Take a wad of cotton wool or paper towels, and spread around a thin layer of oil.
The heat should be about medium-low. Spread 1/3 to 1/2rd of the batter in a circle on the pan. If this is your first time, go with the smaller size to make flipping easier.
Place 2 to 3 strips of pork as flat as possible on top of the batter.
Put on a lid, and let it steam-cook for about 5-6 minutes.
When the pork has lightened up in color, it’s time to flip the okonomiyaki.
Take two spatulas and flip the thing over carefully. Voila! Continue cooking without a lid for about 3-4 more minutes. Lower the heat if it’s cooking too fast, or turn it up a bit if it isn’t. Try to resist the urge to press down on the okonomiyaki at this point - doing so will squeeze some air and fluffiness out of the okonomiyaki.
Flip over once more, so the pork side is facing up. Brush with the sauce of your choice - straight okonomiyaki sauce, a mix of okonomiyaki sauce and mayonnaise, soy sauce, etc.
Sprinkle on some katsuobushi and aonori liberally.
To serve, cut into 4 pieces (the pro does this on the plate with a spatula, but you can use a knife on a cutting board).
The inside should be just cooked through, not doughy or runny. Eat while piping hot. (Okonomiyaki is edible enough when it’s cold, but it’s one of those foods that is so much better when it’s freshly made.)
A Hiroshima-style okonomiyaki is either two of these with some yakisoba (pan-fried noodles) in between, or one of these as a base, topped with a mound of yakisoba, and then a fried egg. One Hiroshima-style okonomiyaki comes in at around 1000 calories. Enjoy.
You can omit the pork belly slices. You can try substituting bacon, but that would flavor the whole thing.
You can get okonomiyaki mix, which has flour, nagaimo powder, dashi, and things already in there. You just add water, or water and egg, depending on the kind. But, that’s not nearly as much fun.