May substitute other meats, lamb is traditional. Other options for thickening stew include making a slurry with cornstarch/water, flour/water, tapioca flour/water and adding at the beginning of the simmering step. Adding cabbage or turnips can add a different flavor profile but is still traditional in Irish cooking.
Check seasonings, add salt and pepper to taste, then remove from heat, stir in parsley and the cornstarch (mixed into 4 teaspoons water) and stir. Cook over low heat for a few more minutes to thicken. Serve with plenty of Irish brown or white soda bread, tea and more Guinness if you like. "A very traditional irish stew by way of Killarney County.
Parsley and/or thyme seem to be common herbs in most recipes and only salt and pepper are used for the spices. This is a stew where the vegetables and lamb are the real stars. The addition of turnips or cabbage can further add flavor with the absence of spices. While mutton or lamb is the traditional meat for Irish Stew, some people prefer beef.
Turnips work really well in this lamb stew, and I've also added some mushrooms – because I love the way they get more deeply savory the more you cook them! Start by adding boneless lamb stewing meat, a peeled and chopped turnip, and sliced or quartered mushrooms to an Instant Pot or slow cooker bowl.