Fill the kettle and boil it. Peel the sweet potatoes. Roughly chop them. Pop the potatoes in a pan. Add enough hot water to cover them. Pop on the lid. Simmer for 20 mins till the potatoes are soft when pressed with a fork.
Sprinkle the flour on a plate. Season with salt and pepper. Dip the haddock fillets in the flour on both sides to coat them. Put to one side.
Trim the leeks. Slice a cross in the top so you can open them out. Rinse out any grit. Finely slice them. Finely chop the leaves from the parsley sprigs.
Warm 1 tbsp olive oil in a deep frying pan or wok. Add the leeks. Season. Fry over a low heat for 8-10 mins till the leeks are soft but not too coloured.
Take 2 tbsp out of the crème fraîche and put to one side. Add the rest to the leeks with 1 tbsp Dijon mustard. Gently heat for 1-2 mins till everything is warmed through. Cover. Take off the heat.
When the sweet potatoes are soft, drain them. Tip them back in their pan. Mash over a low heat till they are smooth. Stir in the crème fraîche you saved in step 5 and some seasoning. Cover. Put to one side.
Warm 1 tbsp olive oil in a frying pan. Add the haddock fillets. Fry for 2-3 mins. Flip the fish over. Fry for another 2-3 mins till they are golden and cooked through.
Serve the haddock with the sweet potato mash, creamy, dreamy leeks and the chopped parsley.