Put each piece of fish in a large greaseproof paper or multi-purpose cooking bag. Scatter over some leek, peas and a tablespoon of crème fraiche. Season with salt and pepper and set the bag on a plate, tucking the ends under the fish.
Microwave in the bag one at a time on high for 3-4 minutes until the fish is cooked. Meanwhile mix the remaining crème fraiche with the dill, salt and pepper. Tip the fish and vegetables onto a warm plate and top with a spoonful of crème fraiche. Grind some black pepper over the top and serve with new potatoes.