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.