Make a cross incision on the skin of each tomato. Plunge them into boiling water for a few seconds, then immediately refresh in cold water. Peel, quarter, deseed, and chop the tomatoes.
Peel and finely chop the onion.
Sauté the tomato flesh and onion in 2 tablespoons of olive oil with a whole crushed garlic clove, bay leaf, and some salt for 30 minutes on very low heat.
Remove the garlic clove and bay leaf. Blend the tomato mixture into a puree.
Cook the ground beef in 1 tablespoon of oil for 5 minutes, breaking up the meat with a spatula. Add some tomato sauce and continue cooking for 5 minutes.
In a bowl, mix the ground beef with the egg, crumbled ricotta, salt, and pepper. Stuff the uncooked cannelloni with this mixture.
Spread half of the tomato sauce in the bottom of a baking dish. Place the stuffed cannelloni on this layer. Cover with the remaining tomato sauce and grated cheese. Bake at 180°C (356°F) for 30 minutes.
Garnish the cannelloni with chopped parsley leaves.