Chop a white onion finely and fry until golden in some olive oil.
Add some double cream, dijon mustard to taste,black pepper,lemon juice. Then add handfuls of mature chedder cheese and simmer until all the cheese has melted.
Place fish filets i use smoked haddock and cod into a casserole and cover with raw spinach leaves.
Pour over the creamy sauce.
make mash Potato and cover all the above.
Pop in the oven at 180 for 30 mins.