Fish with mushrooms baked with mashed potatoes

This is a kind of fish and mushroom pie with mashed potatoes. Such fish, baked with mushrooms, will serve as a full-fledged dish for the dinner table.

Ingredients

• Champignon mushrooms (washed and cut into quarters) - 230 g
• Skinless cod or salmon fillet (diced) - 680 g
• Boiled milk, hot - 600 g (2 1/2 cups)
• For the top:
• Potatoes (peeled and cut into quarters) - 900 g
• Butter - 25 g (2 tbsp. L.)
• Milk - 150 g (2/3 cup)
• Salt and black pepper to taste
• Ground nutmeg, to taste
• For the sauce:
• Butter, unsalted - 50 g
• Onions, medium size (finely chopped) - 1 pc.
• Celery stalk (finely chopped) - 1/2 pc.
• Wheat flour - 50 g (1/2 cup)
• Fresh lemon juice - 10 g (2 tsp)
• Fresh parsley (finely chopped) - 45 g (3 tbsp. L.)

Directions

1. Turn on the oven to preheat to 200 degrees. Grease a heat-resistant form with a volume of about 1.5 liters with butter, pour the chopped mushrooms and fish into it, salt and pepper to taste. Pour the contents of the form into 600 g of hot milk, cover the form with a lid and place in a preheated oven, cook for about 20 minutes.
2. Remove the fish with mushrooms from the mold with a slotted spoon, and drain the liquid into a separate bowl. Transfer fish and mushrooms back to an ovenproof dish and set aside.
3. Meanwhile, boil the potatoes in salted water until soft, for about 20 minutes. Drain the water from the finished potatoes, mash the potatoes with a potato grinder until puree. Put butter in the puree and pour 150 g of milk. Sprinkle potatoes with salt, black pepper and nutmeg and stir. Set mashed potatoes aside.
4. Prepare the sauce. To do this, melt 50 g of butter in a cast-iron saucepan. Pour onion and celery into a preheated saucepan, fry, stirring occasionally, until soft, but do not discolor. Then add flour, stir and remove the pan from the stove.
5. Gradually pour the reserved milk, in which the fish and mushrooms were prepared, into the pan, stir well. Put the saucepan back on the stove, cook, stirring, until thickened. Add lemon juice and parsley, stir, season with salt and pepper to taste and pour the sauce into the fish and mushroom mold.
6. Put mashed potatoes on the fish with mushrooms and put the dish in a preheated oven, bake for about 30-40 minutes, until the top is golden brown.