Peel the vegetable onions and cut into slightly thicker rings. Separate the egg. Mix egg yolk and milk. Season with salt. Sift 100 g flour on top and mix everything to a smooth dough. Beat the egg white until stiff and fold in.
Heat the oil in a wide pot or in the deep fryer to about 180°C (it is hot enough as soon as small bubbles appear on a wooden skewer).
Put 2 tablespoons of flour on a plate. Turn the onion rings in it and pull them through the dough with a fork.
Fry the onions in portions in the oil until golden brown, turning once. Drain well on kitchen paper and sprinkle with sea salt.