Heat the vegetable oil in a wok, deep saucepan or deep fat fryer to 180'c.
Prepare the tempura batter: chill the water in the freezer until very cold. Once cold break the egg into a bowl and whisk in the water. Add the flour and mix with a spoon or fork very gently making sure not to make the batter smooth and leaving lumps of flour.
Prepare the courgette flowers by removing the stamen inside the flower gently with a small knife.
Wash the flowers and pat dry.
Prepare the aioli: Peel the garlic and mince to a pulp. Mix with the egg yolks and the white wine vinegar. Whisk in (very slowly) the 200ml of olive oil and then season with salt and pepper and a squeeze of lemon juice.
To cook the courgette flowers, dust each flower with plain flour and then dip in the batter. Quickly drop into the hot oil and deep fry for 2 or 3 minutes until golden brown. Remove from the fryer, drain on absorbent paper, season with fleur de sel and serve immediately with a dollop of aioli.
«Make sure that you do not make the tempura batter smooth. It should have lumps of flour in the mixture.»