For the filling, dry-fry the beef in a non-stick pan on a medium-high heat, breaking up with a wooden spoon until browned – about 10 mins. Remove and set aside. Add the oil and cook the onion for 5 mins, until soft. Add the garlic for 1 min more, then tip in the beef and 1½ jars of the passata sauce and the sugar. Simmer for 20 mins while you make the white sauce.
Heat the butter in a small pan. When foaming, stir in the flour for 1 min. Add the milk gradually, stirring all the time to achieve a lump-free sauce, then bubble for 2 mins while stirring. Remove from the heat and stir in the soft cheese with seasoning until dissolved. Set aside, covered with cling film to stop a skin forming.
To assemble, pour the remaining tomato sauce into the base of 2-3 large baking dishes or 12 individual ovenproof dishes or foil containers. Spoon the beef into the cannelloni tubes using a teaspoon and lay on top of the sauce. Pour on the white sauce, then sprinkle with Parmesan. If freezing, allow to cool, then freeze wrapped well in cling film. To eat straight away, heat oven to 200C/180C fan/gas 6 and cook for 40-45 mins until the pasta is tender and topping golden. Defrost frozen cannelloni thoroughly, then cook as above for 50 mins-55 mins (or see tip).