Clean, peel and chop the carrots. Peel and finely dice onion and garlic. Heat 2 tablespoons of oil in a large frying pan. Brown the ground pork in it until it is finely crumbly. Add the carrots, onion and garlic and fry briefly. Add tomato paste, sweat briefly and deglaze with canned tomatoes. Season with Italian herbs, salt, pepper and sugar. Let simmer for about 15 minutes
Melt butter in a pot. Sprinkle flour over it and sweat while stirring. Add milk and stock while stirring, let everything simmer for about 5 minutes. Season to taste with salt and nutmeg. Wash the tomatoes and dab dry. Heat 1 tablespoon of oil in a pan and fry the tomatoes for 1-2 minutes. Season with salt and pepper
Pour about 1/3 of the béchamel sauce into an ovenproof dish (approx. 15 x 24 cm; at least 6 cm high). Place the cannelloni close together vertically in the mould. Spoon about 3/4 of the bolognese into the cannelloni, using a spoon handle to stuff the filling slightly. Spread the rest of the béchamel sauce over the cannelloni. Add the rest of the bolognese and tomatoes. Dice the mozzarella. Mix all cheeses and sprinkle on the casserole. Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: see manufacturer) for 35-40 minutes. If necessary, cover the bottom of the oven with aluminium foil in case anything drips off. Serve garnished with basil if desired