Layer the lamb, onions, potatoes in a casserole dish. Sprinkle each layer with herbs and season each layer. Finish with potatoes on top.
Pour in cold water, cover with a piece of buttered, greaseproof paper then place lid on dish.
Cook for 2 to 2 1/2 hours.
NOTES****You can easily substitute a beef roast for the lamb. Also people often add sliced carrots to the layers. Guinness can be substituted for the water for a richer flavor. If you make any of these changes, you no longer have REAL Irish Stew, you have your version of Irish Stew.
I think this could be done in a Dutch oven.
When I was in Killarney, the stew we had was made with the changes of beef, carrots and Guinness. It was sooooo good. I am going to have to make this over the winter.