I’ve never really been good at making tempura, the quintessential Japanese deep fried dish. My mother’s tempura has always been terrific - crispy, light, and not greasy at all. So, taking advantage of her extended vacation here this year, I drilled her properly on how she makes tempura.
Her method does not rely on special tempura flour (cheap in Japan but expensive or hard to get a hold of elsewhere), or other recently touted additions like vodka or other high-alcohol liquor, so anyone should be able to do it. Just follow the key points listed below.
The light tempura batter is meant to enhance the flavors of the vegetables or shrimp or squid and so on that is being fried, not mask it. So the fresher your ingredients are, the better your tempura will be.
This is a point often missed in other directions for tempura. In order to keep the tempura batter crisp, it’s important to make the surface of the things you’re frying very dry. My mother cuts up her vegetables at least half an hour beforehand, and spreads them out in a single layer on kitchen towels or paper towels and puts them near a sunny window. (Since this article is about vegetable tempura I’ll leave the subject of how to prep shrimp or squid for another time, but squid is actually allowed to dry out for several hours in the refrigerator, and shrimp is patted dry with kitchen or paper towels.)
The flour in tempura batter is just there to hold the other ingredients together. It should not be allowed to develop gluten, which leads to heavy, doughy batter. Therefore, you should always use ice cold water with ice cubes in it for the batter, and not mix it too much. A few ice cubes and lumps of flour floating in the batter are fine - they won’t stick to the food you’re dipping in the batter anyway.
You should keep the frying oil at a constant high temperature. If you put too much in at once, you will lower the temperature, which can make the tempura soggy and oil-logged.
At a tempura-specialist restaurant, your tempura is fried right in front of you and served immediately. They only fry a little bit at a time. That’s the ideal way to do tempura. At home, you could stand at the stove making individual portions for everyone else, but if you don’t want to do that just make a small batch at a time and try to eat it immediately, even if you have to stand up again to fry another batch. (This is why I think tempura is really ideal as an appetizer, rather than a main course, in Western-style meal structures. It’s easier to make appetizer-sized portions and eat it right away.)
There’s not need to keep flipping over your tempura over and over. This just lowers the surface temperature unnecessarily. Let the hot oil do its work! Just flip over once if needed.
If you hold the tempura piece for a few seconds just above the oil, with a bit of the end still in the oil, the oil will drain off a lot better. Then transfer the tempura piece to the draining setup that is explained later. Some people transfer the tempura to a second draining setup (with fresh paper, etc.) to drain off even more oil
With these points in mind, here is my mother’s tempura recipe.
For 2 main dish or 4 appetizer portions
Use whatever seasonal vegetables you have. These are what we had in late June in southern France. See the end for some other vegetable suggestions.
For the batter:
Oil for frying (My mother prefers rapeseed oil (natane abura 菜種油). You can also use sunflower, corn or peanut oil.)
Cut the sweet potato into rounds with the skin on. Take the blossom end off the eggplants, and slice into wide strips lengthwise. (If you have a fat Western style eggplant, cut into rounds as with the sweet potato.) Leave the baby zucchini whole, just cutting off the blossom ends; cut regular zucchini into wide strips. Leave the shiso leaves whole. Cut the carrot into matchsticks. Leave the green beans whole, just cutting off the tops and tails.
Spread out the cut vegetables into a single layer on kitchen or paper towels, and leave to dry out on the surface for at least half an hour. The uncut baby vegetables and so on should not need to be dried, but should be totally dry on the surface.
Just before you are ready to start frying, mix up the batter. If your egg is a ‘small’ size, use 250 ml of ice water (or 5 times the amount of egg). If you have a ‘large’ egg you’ll need a tad more water. Mix the egg and water together, then add the flours, mixing rapidly with chopsticks or a fork. Do not try to get rid of all lumps, and floating ice cubes are fine - they’ll help to keep the batter cool.
Pour the oil into a suitable container, no more than 1/3th of the way full for safety. A tip here: Use a heavy pot that retains heat well. A cast iron enamelled pot such as Le Creuset is ideal. In Japan, most people deep fry in a wok - a proper wok made of iron is good because it retains heat well. Don’t use a cheap thin pan. For very small amounts you can also use a frying or sauté pan with fairly high sides. (Neither of us owns a dedicated deep fat fryer nor do we want to make the space for one in our kitchens.)
Heat up the oil. You can use a thermometer if you like, in which case you should heat up the oil to about 175°C or 350°F. Otherwise you can see if the oil is hot enough by dropping a bit of batter in the oil. If the batter blobs drop down and them come shooting up to the surface immediately, the oil is hot enough.
Make ready a large plate or tray lined with newspapers covered with kitchen towels, or a draining rack.
Larger pieces or whole vegetables should be dipped in the batter individually; smaller pieces like the matchstick carrots or the green beans are usually fried in little bundles, dipped in the batter and then into the oil with chopsticks. Start with the more delicate vegetables first, such as the shiso leaves, which only take a few seconds. Proceed to the harder vegetables, ending up with things like the sweet potato slices. Don’t overcrowd the oil pot - be patient, and only do 3 to 4 pieces at at time!
The amount of time each thing should be cooked depends on the vegetable. As mentioned, very delicate thin things only need a few seconds, while hard vegetables need a few minutes. You’ll learn how long things need to be fried by experience, but if you’re not sure just take a piece and cut or bite into it.
Drain each piece on the prepared draining plate or try. Don’t stack the pieces on top of each other, or the pieces underneath will just soak up the oil from above!
Serve tempura when it’s piping hot, for maximum crispiness.
Tempura is often served on a piece of absorbent paper called a kaishi (懐紙), folded attractively. You can use a piece of plain, unprinted paper with absorbent qualities, such as untreated drawing paper (which is what I used in the photo above), plain white paper napkins, and so on. Otherwise, just arrange it attractively on a plate.
For vegetable tempura, my favorite condiment is just some sea salt, sprinkled on. You could add a few drops of lemon juice too, though this isn’t traditional. You can also use tentsuyu, which is just a slightly thinned out version of soba tsuyu or soba dipping sauce  (thin out with a bit of dashi stock). Grated daikon radish is often added to tentsuyu.
Leftover tempura can be crisped up in a toaster oven or regular oven. Just spread out in a single layer and bake for about 5 to 10 minutes until it’s a slightly darker shade of brown.
Japanese people love soggy-on-purpose tempura too, especially in the form of tendon, which is just tempura on top of rice with some mentsuyu poured over it in its simplest form. Tendon is best made with freshly fried tempura, but you can use leftover tempura too.
Basically, anything that is in season can be used. Harder vegetables should be cut thinner or smaller so that they cook faster. Some examples, both traditionally Japanese and not so traditional:
Not very traditional: