Heat ghee/oil in a large frying pan/cast iron pot over medium-high heat. Add onion, garlic, carrot & celery and cook, stirring, for 5 minutes or until softened.
Add lamb mince & rosemary (& optional liver if using) cook for 8 minutes, stirring frequently with a wooden spoon to break up lumps.
Stir in drained beans, flour and bone broth and bring to the boil. Reduce heat to low and simmer with the lid on for about 30 minutes.
Preheat the oven to 180C fan-forced. Place a large pan of water (with a pinch of salt) on the heat and bring to the boil.
Cut the potatoes/pumpkin into 3cm chunks, and the cauliflower into florets. Cook just the potatoes/pumpkin in the boiling salted water for 10 minutes, add the cauliflower for 10 more minutes, or until cooked through, drain well, mash with the milk and grated cheese, and season to perfection.
Check the consistency of the mince – you want it slightly wetter than a bolognaise mince, as it will thicken further in the oven. Add the Worcestershire sauce, taste, and season.
Place the mince mixture into an ovenproof 8-cup (approximately 20cmx20cm) casserole dish.
Sprinkle the frozen peas over the mince, letting them sit on the surface to help prevent the mash from sinking in too much. Put spoons of mash randomly on top and spread around, using a fork to scuff it up and make valleys and mountains, increasing the surface area, and the crispy bits.
Bake for 50 minutes, or until golden and bubbling. Nice with seasonal greens.