- Preheat oven to 375 degrees F.
- Heat oil in a large sauté pan over medium heat. Add lamb and cook until no longer pink. Reserve 1 tablespoon rendered fat and drain meat. Add reserved fat back to the skillet and place over medium heat. Add carrots and 2 cups chopped onions, stirring occasionally, until vegetables start to soften, about 5 minutes. Stir in tomato paste and cook for a minute. Stir in flour and cook for another minute.
- Add lamb back to pan along with Worcestershire, beer and chicken broth. Bring to a low boil and cook until liquid is reduced to a thick gravy, about 15-20 minutes. Season to taste with salt and pepper. Remove from heat and stir in peas. Spread meat mixture into 9 x 13 pan.
- Cook potatoes in boiling water about 20 minutes or until very tender; drain well and mash with skins on, adding milk and 3/4 teaspoon salt.
- While potatoes are cooking, melt 6 tablespoons Kerrygold Salted Butter in a large skillet. Add remaining 1 cup onion; cook 10 minutes, stirring occasionally, until very soft. Add cabbage; cook and stir for 5 minutes more or until very soft.
- Stir cabbage mixture and Kerrygold Dubliner Cheese into hot potatoes and season with pepper. Spread Colcannon on top of lamb mixture in casserole dish.
- Melt remaining 2 tablespoons Kerrygold Salted Butter and brush evenly over Colcannon. Place casserole dish on a baking sheet and bake for 30-35 minutes or until edges bubble and potatoes start to brown. Allow to stand 10 minutes before eating.