2) Cover the potatoes with cold water in a pan and add a pinch of salt. Bring to the boil, then simmer for 20–25 minutes or until completely tender when pierced with the top of a sharp knife. Drain in a colander and peel the potatoes while they are still hot.
3) Meanwhile, heat the rest of the olive oil in a pan. Add the onion, leek, carrot and garlic and saute for 3-4 minutes until just beginning to soften but not colouring.
4) Stir the minced beef into the pan and cook for 2–3 minutes until browned, breaking up any lumps with the back of a wooden spoon. Stir in the tomato puree and cook gently for another 10 minutes until completely tender. Season to taste and keep warm or reheat as needed.
5) Push the cooked peeled potatoes through a potato ricer or sieve using a spatula. Quickly heat the milk in a pan. Beat the butter into the warm mashed potato and then add enough milk to make a smooth puree. Season to taste.
6) To serve, spoon the minced beef mixture into 9cm ring moulds set on warmed plates. Spread over the mashed potatoes, gently fluffing the top with a fork. Carefully remove the moulds. Finish off with the caramelized shallot slices and drizzle around the herb oil. Garnish with the thyme sprigs.