Spinach & potato layer
Whisk together the eggs, milk and flour in a large bowl, season. Grate the potatoes directly into the egg mixture using a roesti grater, mix in the spinach.
Season the fish fillets. Spread one third of the potato & spinach mixture over the base of the loaf tin. Place half of the fish fillets on top. Cover with the second third of the potato & spinach mixture. Arrange the remaining fish fillets on top, cover with the remaining potato & spinach mixture, press the mixture down firmly.
Approx. 35 mins. in the centre of an oven preheated to 220°C.
Mix the crème fraîche with the chervil, season.
Remove the fish cake from the tin together with the baking paper, cut into approx. 2 cm slices, serve with the sauce.