Cut pasta into 5-inch squares and parboil in water for a minute or a minute and a half. Transfer to a bowl of cold water. Spread in one layer over cloth towels. Make Bechamel Sauce: Melt butter, stir in flour and add milk slowly. Heat until mixture thickens. Set aside. Make Spinach: Parboil spinach leaves until just wilted. Drain. Cool and squeeze out moisture and chop. Saute 1/3 cup minced shallots in 2 tablespoons butter. Add parboiled spinach and saute gently until spinach has absorbed butter. Season with salt and pepper. Make Ricotta Filling: Blend ricotta cheese with parmesan. Add eggs and egg yolks and spinach filling. Season with salt, pepper and nutmeg. To assemble: Preheat oven to 400 degrees. Butter a large gratin dish or two smaller ones. (Canneloni are baked in a single layer, snuggly set-in but not overlapping). Spoon some filling down the center of a parboiled pasta square, spread to 1/2-inch of edges, roll up and transfer, seam side down to the gratin dish. Ladle Bechamel over top and sprinkle with 1/3 cup grated Parmesan. Dot with 4 tablespoons chilled cubed butter and bake on upper center rack of oven for 15 minutes or until bubbling. Let stand 15 minutes before serving. Can serve with extra grated Parmesan.
Recipe courtesy of Michele Urvater