Incise the skin diamonds. Put the skin in water for 2 hours, then - dry with paper towels. Carefully rub with salt and pepper. Fry in a roasting pan with vegetable oil on all sides except the skin, remove it. In the same roasting pan fry the onion half rings until golden brown. Top with meat skin side up. Place the roasting pan in a preheated 200 degree oven and cook for 2.5 hours. After 30 minutes from the start baking reduce the heat to 180 degrees Celsius and gradually watered beer. Remove the meat and give it a \"rest.\" Make a puree of onion sauce by blender if it is too thick - diluted with water, season with salt, pepper and nutmeg.