Peel and cut the potatoes into even smaller pieces.
Place them in a medium pot of cold water with a tsp of salt. Bring to a boil over high heat and cook the potatoes until they are tender.
Once potatoes are cooked, transfer them to a bowl. Add in butter, milk, egg yolk and 1/2 tsp of salt and black pepper and mash the potatoes until smooth. Set aside.
Heat olive oil in a pan over medium heat and saute chopped onions for 2-3 minutes.
Followed with crushed garlic and chopped carrot, saute until carrots are tender (about 5-7 minutes).
Add in ground lamb and cook for about 5 minutes or until meat are no longer pink. Season with 1/2 salt and black pepper, chopped rosemary and thyme.
Then add in tomato paste and flour. Stir until well-combined before adding in beef broth and peas. Bring the mixture to a simmer then reduce heat to low and continue cooking until sauce thickens (stirring occasionally).
Preheat oven to 200°C.
Layer the meat mixture evenly in an ovenproof dish then spread the mashed potato over the meat mixture.
Baked at 200°C for 20-25 minutes or until the mashed potato is golden brown.