Cut the onions in big pieces as well as the mushrooms.

Put them in a pan with olive oil and start to cook them at a low fire.

Add the chicken leg with the skin looking to the fire. 
Put up the fire for a little while.

When onions and mushrooms are cooked, add some white wine or beer to the mix.
Put the fire low and cover the pan. 

Let it cook for 30 minutes.

Serve with rice.