Bring 3-4 quarts of water to a boil. Slice 4-6 Yukon Gold potatoes into 4ths and add to water when boiling. Allow them to boil for 15-20 minutes, checking for doneness with a fork after 15 minutes.
Grate 1 cup Dubliner cheese, slice 8 oz. baby bella mushrooms, dice 1 large carrot, and dice 1 large red onion. You can combine carrots and onions, but keep mushrooms separate.
Add carrots and onions to a large sauté pan with 2 tbsp. olive oil. Sauté for 7-10 minutes until onions are tender and lightly brown. Remove from pan. Add 2 tbsp. olive oil to the sauté pan and sliced mushrooms. Sauté until brown, about 5 minutes.
Once mushrooms are brown, add 1 pound ground lamb. Sauté until brown, then add 1 tsp. black pepper, ½ tsp. salt, 1 tsp. garlic powder and leaves from 3-4 sprigs of fresh thyme. Add back carrots and onions with 2 tbsp. butter, 1 cup frozen peas and 2 tbsp. flour. Stir until butter is melted.
Preheat oven to 400 F. (204 C.)
By this time, potatoes should be ready. Strain and allow them to steam off while you continue with the filling.
To the pan, add 1 cup red wine, 1 cup beef stock, 1 tbsp. tomato paste and 3 tbsp. Worcestershire sauce. Stir and allow liquids to reduce into a sauce. About 8-10 minutes.
While sauce thickens, mash potatoes with a potato masher. Add a sprinkle of garlic powder, salt and pepper to taste, grated Dubliner cheese and ½ cup heavy cream. Depending on the size of your potatoes, you may need to add more cream to get them to a nice, smooth texture.
Once sauce has thickened, remove from heat and spoon into an 8"x8" pyrex dish or oven-safe bowls. Pipe or spoon mashed potatoes onto the meat filling and brush with 1 beaten egg. Sprinkle with a little more Dubliner cheese and bake for 20 minutes, then broil for 5 minutes – or turn heat to 550 F. (287 C.) if you don’t have a broil function. Carefully remove and serve.