In an 8- to 10-inch enameled or stainless-steel skillet, melt 4 tablespoons of butter over moderate heat. Add the chopped fresh or frozen spinach and cook, stirring constantly, for 2 to 3 minutes, or until almost all of the moisture has boiled away and the spinach begins to stick lightly to the skillet. Now add the 3/4 cup of ricotta cheese and cook, stirring, for 3 or 4 minutes longer.

With a rubber spatula, transfer the entire contents of the skillet to a large mixing bowl and mix in the 2 lightly beaten eggs, 6 tablespoons of flour, 1/4 cup of the grated cheese, 1/2 teaspoon salt, pepper and nutmeg. Place in the refrigerator for 30 minutes to 1 hour, or until the gnocchi mixture is quite firm.

Preheat the broiler. Bring the 6 to 8 quarts of water and 1 tablespoon of salt to a simmer over moderate heat in a large soup pot or saucepan. Flour your hands lightly and pick up about 1 tablespoon of the chilled gnocchi mixture at a time. Shape the tablespoonfuls into small balls about 1 1/2 inches in diameter. Gently drop the balls into the simmering water and cook them uncovered for 5 to 8 minutes, or until they puff slightly and are somewhat firm to the touch. With a slotted spoon, lift the gnocchi out of the water and set them aside on a towel to drain.

Now pour 2 tablespoons of the melted butter into a shallow 8-by-12-inch flameproof dish and swirl the butter around until the bottom of the dish glistens. Arrange the gnocchi in the dish in one layer about 1/4-inch apart, dribble the remaining 2 tablespoons of melted butter over them, and sprinkle the gnocchi with the remaining 1/2 cup of grated cheese. Set under the broiler 3 inches from the heat for 3 minutes, or until the cheese melts.

Serve the gnocchi at once, directly from the baking dish. Serve additional grated cheese separately, if you wish, Or, if you have a small grater, suitable for your table, pass a small chunk of Parmigiano-Reggiano with the grater for diners to add cheese as they like.