Cook sweet potatoes and potatoes for approx. 20 minutes until cooked. Drain the water and mash the potatoes to a smooth puree. Steam the shallots and garlic in the oil over low heat until translucent, add the chilli, white wine and cream and reduce to a third. Pass through a sieve, bring to the boil and stir in the mashed potatoes. Then stir in butter and coriander and season with salt and pepper.