Knead the fat in flakes, flour, hazelnuts, 1/4 teaspoon of salt, 1 egg and 1 tablespoon of cold water to a smooth dough. Cover and chill for about 30 minutes. Meanwhile, hard-boil 7 eggs for about 10 minutes.
Then rinse with cold water, peel and chop. Clean and wash spring onions and cut into rings. Whisk remaining eggs and 1 cup of crème fraiche. Season to taste with salt, pepper and nutmeg.
Roll out dough between 2 layers of foil (26-27 cm Ø). Place in a greased mould with removable base (24 cm Ø). Press down the edges. Pre-bake in the preheated oven (electric: 200°C/ gas: level 3) for 10 minutes on the bottom shelf.
Then add chopped eggs, spring onions and egg cream. Bake for a further 40-45 minutes on the middle rack (electric oven: 175°C/ gas: level 2). Serve each piece with a dollop of crème fraîche and trout caviar.
Results in about 8 pieces.