Steam the sole or sauté it quickly. Drain well, then finely chop.
Melt the butter in a large skillet over medium heat. Add the onions and cook until tender. Add the spinach; cook until completely wilted. Transfer to a sieve and drain well. Chop the spinach mixture and squeeze dry. Mix the sole, spinach mixture, eggs, bread crumbs, and nutmeg. Season to taste with salt and pepper. Add more bread crumbs if the mixture is wet.
Roll, fill, and cut the ravioli as directed on, using
Heat a large pot of salted water to boiling. Heat the tomato sauce in a wide saucepan. Drop in the clams, cover the pan, and cook until they open, 5 to 7 minutes. Keep warm.
Drop the ravioli into the boiling water and simmer 4 to 5 minutes. Remove them with a slotted spoon or large skimmer. Shake off the excess water and place on serving plates. Spoon the tomato sauce with clams over the ravioli and sprinkle with parsley. Serve hot. No cheese, please.