Turn on the oven to preheat to 200 degrees. Prepare a kitchen processor for making the dough. Add flour, salt, and butter to the processor bowl. Pulse until a crumpled mass is formed. Pour about 8 teaspoons of cold water into the processor. Pulse until a homogeneous dough is formed. Place the dough on plastic wrap, form a ball, wrap in plastic and refrigerate for 30 minutes.
Take the dough out of the refrigerator and roll it into a layer, put it in a mold with a diameter of about 20 cm, forming sides. Crack the dough with a fork and bake for 20 minutes.
Meanwhile, put fish fillets in milk, add black peppercorns and thyme. Soak for about 10-15 minutes. Remove fish from the milk and cut into small pieces. Put the milk in the refrigerator.
Stir the cream with the eggs, then add the cooled milk, mix well.
Remove the cake from the oven, put the chopped fish, potatoes in an even layer, season with salt, pepper and pour the creamy mixture, put in the oven, and bake for about 40 minutes.