Preheat the oven to 220°C (425°F, gas mark 7). Cut the carrots and parsnips across in half. Cut the narrow halves in half lengthways and each of the larger halves into quarters lengthways. Place the prepared vegetables in a saucepan and pour in just enough water to cover them. Bring to the boil, then reduce the heat slightly and partly cover the pan. Cook for 2 minutes.
Meanwhile, mix together the lime juice, oil, coriander, cinnamon and pepper to taste in a large roasting tin. Cut the sweet potatoes across in half, then into thick wedges, about the same size as the pieces of carrot and parsnip. Add the sweet potato wedges to the tin and turn them in the spice mixture until they are well coated, then push them to one side of the tin.
Drain the carrots and parsnips and put them in the roasting tin. Use a spoon and fork to turn the hot vegetables and coat them with the spice mixture. Place the roasting tin in the oven and bake for about 40 minutes, stirring and turning the vegetables twice, until they are browned in places and tender.
While the vegetables are baking, make the dip. Mix together the mustard, sugar and lime zest, then stir in the yoghurt and dill. Transfer the dip to a serving bowl, cover and set aside until the vegetables are ready.
Remove the vegetable wedges from the oven and leave them to cool slightly. Garnish the mustard dip with a little extra dill, and serve with the vegetables.
Some more ideas
Chilli and herb dip: Mix plain low-fat yoghurt with 1 small fresh green chilli, deseeded and finely chopped, 1 tbsp chopped fresh mint, 2 tbsp chopped fresh coriander and the grated zest of 1 lemon. Use the juice from the lemon in the mixture for coating the vegetables instead of lime juice. *Coat the vegetables with a spice mixture made from lemon juice instead of lime juice, 1 tbsp caraway seeds instead of coriander seeds, and ½ tsp ground mace instead of cinnamon. Use lemon zest instead of lime zest.
Parsnips were eaten by both the Greeks and the Romans, but the variety common today was not developed until the Middle Ages. Parsnips were an important staple food before the introduction of the potato.