Prepare your baby squid by patting it dry with a kitchen paper to soak up any excess moisture, as if it is wet when it goes into the oil it will spit everywhere which is dangerous. Take particular care with the tentacles if you are using them, as they are good at harbouring moisture.
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Make your tempura batter by quickly whisking ice-cold sparkling water into the tempura flour. Add the lemon zest and season with salt and pepper but do not over stir the batter as gluten will start to form, which in turn will make the popcorn calamari chewy rather than crispy.