Begin by prepping your veggies. Peel the turnips, radish, and carrot and cut into small cubes. (Make this size decision for yourself. Think about what would look nice on a fork with minced lamb and peas. Think relatively small.) Finely chop the onion.
In a heavy-bottomed pot over a moderate heat, add a glug of olive oil and the chopped onion and carrot. Allow them to sweat and cook down for about 5 minutes, or until they have softened a little and the onion is going translucent. While this cooking is happening, cube the potatoes and peel and couple cloves of garlic (you can also add any other root veggie you’d like to the mash topping--and if you choose to, do that prep now too.)
Add the other cubed veggies (turnips and radishes,) season well with salt & pepper, and give everything a good stir.
Get a big pot of salted boiling water and add the cubed potatoes, any other root veg you want and garlic (if using) cooking. (The smaller the cube the faster it cooks!) And remember: you can’t over cook the mash topping--the mushier they are the easier it is to mash. Cook until fork tender.
After the pie filling veggies have had a good start add the minced lamb and break up with a wooden spoon or spatula. Add a little more salt & pepper to the pot, and a few dashes of Worchestershire sauce (if desired) and rosemary, and stir well. Cook until the lamb is brown.
When the potaotes for the mash topping is fork tender, drain and then add a pad of butter and good splash of milk. Mash, adjusting the milk if needed for a looser mash (do this all by eye and feel. It’s easy.) Taste and adjust seasoning and add more butter if you like. Preheat the oven to 400F.
Assemble the pie: in a large baking/pie dish or individuals, add the filling and the spread the potato topping on top. Garnish with a stem of rosemary and pop in the oven.
Cook until some of the potato catches and gets crispy on top, it smells amazing, and the filling begins to bubble around the edges. Allow to sit for about 5-10 before digging in and serving. A great accompliment: string beans!