Preheat oven at 400 °F (205 °C). In a pan, heat butter at medium heat. Cook leeks for 2 to 3 minutes. Remove from heat and cool down.
Add egg, ham and, if desired, basil. Salt and pepper. Stuff cannellonis with the preparation. In a gratin plate of 33 cm x 23 cm (13 inches x 9 inches), pour half the tomato sauce and set cannellonis. Cover with remaining tomato sauce and mozzarella.
Cover with aluminium paper and oven bake for 25 to 30 minutes. At mid-cooking, remove aluminium paper.
Did you know that...
Every year, we plant millions of Quebec leeks in the spring, which we harvest from mid-August onwards.