Fish casserole with mustard sauce

Traditional recipe from The Netherlands

For the casserole:

• 2 large sliced onions
• 2 tbsp of butter or margarine
• 500g of boiled fish (whiting, cod, plaice or frozen fish)
• lemon juice
• Dutch mashed potatoes

For the mustard sauce:

• 1 1/2 cup of fish stock
• 1/2 cup of flour
• 2 tbsp of butter or margarine
• mustard

Bring the fish stock or water to the boil.

Mix the flour with a little water to a smooth paste and pour into the sauce liquid, stir until it thickens.

Add butter or margarine and mustard.

Fry the onion to golden brown.

Put the bits of fish on the bottom of a casserole. Sprinkle some lemon juice and alternate a layer of mashed potatoes with a layer of onions and a layer of fish and mustard sauce. Make sure to end with a layer of mashed potatoes.

Put the dish in the oven and brown on top.