Heat the dripping in a large saucepan and cook the onion for 5 minutes.
Heat olive oil in a frying pan and brown the lamb mince while breaking up lumps.
Stir flour into the onions followed by bay leaves, thyme, and anchovy.
Add tomatoes, 450ml stock, and Worcestershire sauce to the onion mixture.
Combine the mince with the sauce and simmer for 45 minutes after seasoning with salt and pepper.
Preheat the oven to 200°C.
Boil the potatoes for 10 minutes until tender.
Drain potatoes and mash with milk, butter, egg yolk, salt, and pepper.
Transfer meat to a 1.4 litre dish and spread the mash evenly over the top.
Bake in the oven until the surface is golden-brown.