Add your flavourless oil and your carbonated water, whisk till it's incorporated and slightly lumpy. This will be a thin batter (consistency of double cream) which is perfect to keep your tempura light and crisp
Heat your oil over a medium heat, a good way to know when it's ready is to stick the back of a wooden spoon in and you should see some consistent gentle bubbling
Dip your veg of choice and fry until golden
Notes
In all honesty, when I tempura I rarely measure this out exactly, so if you feel confident just eyeball your plain flour, add cornflour which should be roughly about a 1/3rd of your plain flour measurement, salt, and your baking powder. Then add your oil and gradually add your carbonated water until a thin batter, whisk briefly until incorporated. Do not keep whisking until this is lump free as this will activate gluten.For dipping sauces, go for some sweet chilli sauce or my go-to which is light soy mixed with mirin, a touch of rice vinegar and a little shiitake dashi
Keyword batter, how to, mushrooms, tempura, tempura batter