Preheat oven to 375°f. Butter a 9x13-inch baking pan. bring a large pot of salted water to a boil. add spinach and cook 1-2 minutes until wilted drain.
Squeeze excess water from spinach and set aside. Béchamel sauce: heat milk in a small saucepan. Bring to a boil and remove from heat.
Melt 2 tablespoons butter in a medium saucepan. Add flour and cook for 2 minutes stirring constantly. Whisk hot milk into flour mixture. Bring to a simmer, whisking frequently.
Season mixture with salt, pepper and nutmeg to taste set aside. Process spinach, veal, half of the Parmigiano cheese and ham in food processor until coarsely chopped. Season mixture with salt and white pepper.
Beat eggs in medium bowl. Add spinach mixture to eggs. Mix well. Bring a large pot of water to a boil. Cook Lasagne sheets for 3 minutes. Drain and spread flat on a baking sheet.
Pour 1 cup of the béchamel sauce in prepared baking dish. Spoon 2 tablespoons of filling at one end of each Lasagne sheet. Roll and place in prepared baking dish.
Spread remaining béchamel sauce over Cannelloni. Drizzle veal stock or demi-glace over sauce. Dot with remaining butter and sprinkle with Parmigiano cheese. Bake for 30 minutes. Let rest 10 minutes before serving.