For the mayonnaise, place the egg yolks, mustard, garlic, a pinch of salt and the oil in a tall, slim container. Starting at the bottom and working upwards very slowly, blend with a stick blender until thick. Taste for salt. Add the lemon juice and whizz until very thick. Transfer to a piping bag.
To cook the shrimp, bring a large saucepan of water to the boil. Add the salt and lemon ju