Melt butter in a large saucepan over low heat. Add onions to the saucepan and cover. Cook for about 30 minutes, stirring occasionally.

Set heat on medium-high. Add beer and cook, uncovered, for 5-10 minutes, or until beer is reduced by about half.

Add the beef broth and the Worcestershire sauce. Heat the broth mixture until it boils. Reduce the heat to low. Cover the pot and simmer for about 30 minutes.

Meanwhile, toast or bake the garlic bread according to package instructions.

Divide the soup between 4 bowls. Place one piece of toast on top of each bowl. Top each piece of toast with ¼ c. of Irish cheddar cheese.

Place bowls of soup on a baking sheet and broil in the oven for a few minutes, or until cheese is melted and golden brown.