Cut the onions into thick slices and separate them carefully without breaking the rings.
Pour the flour and a teaspoon of salt into a bowl. Then, little by little, pass the onion slices through this bowl to mix them with the flour and then reserve them on a plate for later. If you find the onion flavor too strong, you can lower it by first dipping the onion slices in salted water for at least 10 minutes.
In a second bowl, beat the egg together with the milk and a pinch of black pepper until you get a homogeneous mixture.
Add this last mixture of milk and egg in the bowl along with the flour and beat with a hand mixer until everything is well mixed.
Put a normal skillet or a wok pan over medium heat with enough oil to cover the onion rings. Meanwhile, fill a bowl with breadcrumbs to prepare the fry.
When the oil is hot, dip the onion rings in the egg, milk, and flour mixture, then roll them over with the breadcrumbs. Next, fry them in the pan for a couple of minutes, until they are brown and crisp on both sides.
Repeat this last step for all the rest of the onion rings. Place the ones that are already brown on a plate with several layers of absorbent paper or kitchen paper, to remove excess oil.