Make the bechamel sauce to a thin consistency, like sour cream, and keep it warm over very low heat.
For the filling, cook the onion in 1 tbsp (14 g) butter until translucent. Add the ground beef, lower the heat, crumble it, and cook without browning. Once it loses its raw red color, cook 1 more minute.
Move the meat to a bowl with a slotted spoon, leaving the fat behind. Add salt, chopped ham, egg yolk, about 1/8 tsp nutmeg, grated Parmesan, ricotta, and 1/4 cup of bechamel. Mix well and correct seasoning.
For the sauce, cook the onion in 2 tbsp (28 g) butter until pale gold. Add the beef, crumble it, cook until it loses its raw color, then add salt and the tomatoes with their juice. Simmer at the slowest bubble for 45 minutes, stirring occasionally. Correct seasoning.
Roll the pasta very thin and cut into rectangles about 3 x 4 inches (8 x 10 cm).
Boil water and, following the method used for lasagne sheets in the book, parboil the pasta briefly, cool it, and spread it on cloth towels.
Preheat the oven to 400 F (205 C).
Butter the bottom of the baking dish.
Spread 1 tbsp bechamel on a dinner plate. Coat the underside of a pasta rectangle by rotating it over the bechamel. Spread about 1 tbsp filling thinly on top, leaving a 1/2-inch border. Roll up jelly-roll style and place seam-side down in the dish. Repeat, packing snugly but not overlapping.
Spread the meat sauce evenly over the cannelloni. Spread the remaining bechamel over the sauce, sprinkle with the 1/3 cup Parmesan, and dot with butter.
Bake on the top rack 10 to 15 minutes, no longer than 15, until lightly golden. Rest at least 10 minutes, then serve from the dish.
