Slice the onions into 1 cm thick rings. To make the filling easier, only pair up every second ring.

Wrap thin slices of cheese and ham (or bacon) inside of the bigger onion rings.

Then place the smaller onion rings in their place.

Coat the filled onion rings in the flour, then in the egg yolk, and finally in the breadcrumbs.

The only thing left to do is to fry them in hot oil,  then you can serve them.

Good luck with making the recipe, and have a nice meal!