1Heat olive oil in a large, deep sauté pan over medium heat. Add the onion, carrot and celery and cook, stirring occasionally, for 5–7 minutes or until softened. Add garlic and cook for 1–2 minutes or until fragrant.
2Increase the heat to medium-high and add the ground beef, salt and pepper. Break up the meat with a wooden spoon and stir for 4 minutes, until meat is cooked through but not browned.
3Add the vinegar and cook, stirring occasionally, until it has almost evaporated. Add the sugar, crushed tomatoes and tomato paste and stir to combine. Bring to a boil, then reduce heat and simmer, uncovered, for 20 minutes. Remove pan from the heat, stir in the basil and set aside.
4Melt the butter in a medium saucepan over medium heat until foaming. Add the flour and cook, whisking constantly, for 1 to 2 minutes or until mixture bubbles and begins to come away from the side of the pan. Remove the pan from the heat and add the milk all at once, whisking constantly to avoid any lumps. Return the pan to the heat and bring to a boil. Reduce heat to medium-low and simmer, stirring constantly with a wooden spoon, for 7–10 minutes or until sauce thickens and coats the back of the spoon. Remove from the heat and stir in the grated Parmesan, salt and pepper.
5Spread ¼ of the meat sauce (about 2 cups/480ml) evenly on the base of a 9 x 13-inch baking dish.
6Place 4 of the lasagna sheets over the sauce (they will overlap slightly). Spread another ¼ of the sauce over the pasta followed by 1/3 of the béchamel (about 1½ cups/360ml). Continue layering the pasta, meat sauce & béchamel twice more, finishing with the béchamel. Sprinkle with grated Parmesan.
7Insert wire rack in rack position 6. Select BAKE/375°F/CONVECTION/30 minutes. Press START to preheat oven.
8Once preheated, place lasagna in the oven and cook for 25–30 minutes or until bubbling and browned on top.
9Let rest for 15 minutes before cutting and serving.