It is important to remember that the cannelloni are pre-cooked and for this reason they are filled with a soft filling and then covered with a light, liquid sauce. Only in this way will the cannelloni be able to cook properly, by absorbing the humidity of the sauce, they will swell and cook until they are "al dente". They are baked in the oven at 180 gradi. Never fill the cannelloni the day before as they could become too wet. To check whether the cannelloni are cooked, just pierce the surface with a fork.Melt the butter over a low flame in a non-stick pan then add the chopped onion, celery and carrot and brown. Add the meat. Pour over the red wine and leave to evaporate. Season with salt and pepper and warm through. Add the sieved ricotta to make a soft but dry mixture. Fill each cannellone inserting the filling from the ends. Place on a buttered baking dish and cover with tomato sauce. Sprinkle with Parmesan cheese and bake at 180 gradi for 20 minutes.