Once you turn off the heat the stew will start to cool and will thicken. If you find you want it thicker still, add a little instant mashed potatoes to help thicken.Traditionally, Irish Stew is served with lamb or mutton. Here in the United States, in South Louisiana especially, it's not so easy to get lamb - if you can find it you need to take out a second mortgage to buy it. Beef stew meat is an acceptable alternative.