Place the flour, eggs, salt and butter in a bowl and knead to a smooth supple dough. Cover the dough and leave to rest for 20 minutes.
For the filling, cut the sole or cod fillet into pieces and freeze for 30 minutes.
Meanwhile, wash the spinach, blanch for several seconds in boiling salted water, drain, rinse in cold water, then drain and lay the leaves to dry on a tea towel.
Blanch the parsley briefly in the boiling water, rinse in cold water and drain.
Place the fish, cream, sour cream and parsley in a blender.
Blitz to a fine paste. Season with salt, pepper, lemon zest and juice.
Roll out the dough in batches on a floured surface into a long strip, about 10cm wide. Cover with the spinach leaves, leaving a border free all the way around.
Put the fish mixture into a piping bag with a large plain nozzle and pipe blobs in the middle of the spinach.
Brush the dough edge with water, fold the strips over the filling and press well at the edges to seal.
Using a pastry wheel, cut into ravioli. Press the edges well.
Bring the stock to the boil. Cook the ravioli in the stock for about 3 minutes until tender.
Remove with a slotted spoon and place on plates. Mix about 4 tbsp of the stock with the sour cream. Drizzle over the ravioli, top with carrots and parsley and serve.