Bring a pan of water to the boil and add new potatoes and a pinch of salt. Simmer them for around 10 minutes, until tender.
In a large pan, add the haddock fillets and milk (add parsley stalks if you have some). Bring it to the boil, cover and leave to gently simmer for 3-5 minutes.
Take the pan off the heat but leave the fish in the pan to continue to steam for another 5 minutes, after which the fish will flake when a fork is pressed into it.
Place the fish on warm plates and set them aside. Set a colander on top of the potatoes and add the carrots to steam for 2-3 minutes, whilst making the sauce.
Mix the cornflour with 2 tablespoons of water. In a small pan, bring the milk from the fish to the boil and add the cornflour mix. Stir continuously until the sauce thickens. Stir in the capers, most of the parsley, and season.
Spoon the sauce over the fish or around the plate. Serve with carrots, potatoes and a sprinkle of leftover parsley.