Preheat the oven to 190°C, fan 170°C, gas 5. Put the beetroot and parsnip in a small, non-stick roasting tin, cover with foil and bake for about 45 mins until very tender. When the beetroot is cool enough to handle, peel off the skin.
Meanwhile, put the lamb in a pan and cover with the vegetable stock. Simmer for 30 mins until the lamb is tender.
Remove the lamb with a slotted spoon, then purée with the beetroot and parsnip to make a coarse purée. Loosen with a little of the vegetable stock.
Cook's tip: to freeze, cool completely, then spoon into ice cube trays or individual rigid pots. Freeze, then transfer the cubes to freezer bags for up to one month. Defrost thoroughly before reheating until piping hot.