Add the unsalted butter to a large saucepan and place it over medium heat until melted. Then add the chopped onion and garlic, bay leaves and rosemary.
Stir again. Cook the potato for about 4 minutes. Then add the chicken stock and beer. Season with pepper and salt.
Cover the pan and cook the ingredients over medium heat for about 10 minutes. Then take the pan off the heat, remove the rosemary and bay leaves and blend or mix it into a fine soup.
Add the cream, cooked ham and grated cheese.
Place the soup back over medium heat until boiling and cook it for another 5 minutes. Then check the seasoning and add extra pepper or salt to taste if necessary. Stir in the chopped chervil.
Then take the soup off the heat again and scoop it onto large bowls. Serve hot.