Tempura is a lovely dish when properly prepared and cooked, with a nice, light and crisp batter.
The basic secret is the temperature of the batter and the oil using for deep frying.
The other tip is to just barely mix the batter, for once in your life a lumpy batter is just want you are looking for.
Use a thermometer to get the oil at just the right temperature and cook in very small batches so that the oil temperature does not drop.
The tempura batter needs to be ice-cold. All ingredients should be kept immersed in ice or in the deep freezer until you are ready to cook - this is very important.
► Try using kudzu flour to replace half of the wheat flour.
► Add a cap full of sake to each batch of batter. Apparently, this is a necessity.
► Do not make the batter ahead of time, but make it immediately before you intend to use it
► Do not over mix the batter and only coat the food items with a thin coating of batter (leave the lumps)
► If you are frying both vegetables and seafood - start with the vegetables using a temperature of 340 degrees F (170 degrees C). Then boost the temperature to 350 degrees F (175 degrees C) for the shrimp and seafood
► Using a neutral tasting oil for frying that has a high smoke point. Ideal oils are grape seed oil and rice bran oil, and perhaps peanut oil. Don't use olive oil.
► Make two or more tiny cuts into the stomach side of each shrimp. This will keep it straight when it cooks and shrinks in the oil. Pick up each shrimp by the tail and dip the body into the cold batter just before frying batter.
► For squid, take off the skin and lightly dust the squid pieces in flour, first, as this helps the batter to stick to the squid.
► The tempura batter should be made in small batches and not left to stand.
► Use thick chopsticks or a fork to gently and quickly stir the batter in criss-cross motion. Don't worry about the lumps which are an asset!
For the lime aioli
Mix all the ingredients for the aioli and set aside.
Break the egg into a large bowl, add 1 1/4 cups of ice cold water and whisk gently. Add the 5 ice cubes. Add the bicarbonate of soda to the flour and mix well, dry. Then tip the flour into the egg mixture and mix very briefly into a lumpy batter. Put the bowl on a bed of ice, or place it in the freezer, while you prepare the shrimp.
Heat the oil in a deep saucepan or a fryer to 350 degrees F (180 degrees C). Prepare the shrimp by shelling and removing the vein. Take each shrimp by its tail and lightly dust it in plain flour. Remove the batter from the freezer or ice. Then dip each shrimp into batter and then gently transfer the shrimp into the oil. Fry only one or two at a time. The shrimp generally take about 2-3 minutes depending on their size. When cooked they should be a nice light brown or gold color and very crisp. Drain on kitchen paper.
Serve immediately with the lime aioli some cucumber slices and spring onions.