1 heaped tsp grain mustard (don't use English mustard)
1 or 2 medium onions, sliced thinly
Small bunch fresh chopped parsley or chives
Cut the fish into portions. 150g is a recommended adult portions and 75 - 100 for children.
Place the sliced onions in a dry non stick pan, use a tiny bit of oil if your pan isn't very non stick, cook, till soft, on a medium heat without colouring much.
Add the cream, mustard and 1/2 stock pot, mix well until the stock pot dissolves. Add the chopped parsley or chive and give it a good stir again.
Place the fish in the pan then cover with lid or tin foil, simmer on a lowish heat for 15 minutes or so. This time will vary depending on how thick your fish is. Test it by cutting into the thickest part of one if you need to.
Remove the lid when the time is up the test the fish, if it is cooked place it on the plates, then give the sauce a good stir and pour as much as desired over the fish.