Cookery Art - Halibut and spinach (heilbot met spinazie)

1. Cut off the stems of the spinach. Wash the leaves in cold water and drain. Peel and mince the onion. Sautee the onion in the butter, add the spinach and salt, pepper and nutmeg to taste. Put on the lid and let simmer for 8 minutes. Clean the mushrooms with a brush or cloth, slice them and add to the spinach. Mix the corn starch with a bit of the cream and add to the spinach. Quickly boil the spinach for a minute, turn off the heat and put the pan in the oven at lowest heat.
2. Rinse the fish and pat it dry with paper towels. Use a large pan. Put in 1 litre (4 cups) of lightly salted water and bring to a boil. Add the fish, put the lid on and gently poach the halibut. Do not boil! Take the fish from the water and put it on a heated plate. Garnish with a slice of lemon and a pat of hard butter. Serve the spinach in a separate dish.