1. To make the Bolognese, heat the oil in a large heavy-based saucepan over medium heat. Add onion and garlic. Cook for 5 minutes or until soft. Increase heat to high, add mince, cook, breaking up mince with a wooden spoon, for 5 minutes or until browned. Add tomato paste, Cook, stirring for 1 minute. Stir in tomatoes and sugar. Bring to the boil. Reduce heat to medium-low. Simmer, uncovered, for 40 minutes or until thick. Season with salt and pepper.
2. To make the béchamel sauce, melt the butter in a medium saucepan over medium-high heat until foaming. Add flour, cook, stirring for 1 minute. Remove from heat. Slowly add milk, whisking constantly, until smooth. Return to heat and cook, stirring with a wooden spoon until the sauce comes to the boil.
3. Preheat oven to 180/160 degrees fan forced. Grease a 12-cup capacity lasagne dish.
4. Spread a little béchamel sauce over the base of dish (this prevents the pasta sticking to base). Cover with 1 layer pasta sheets, breaking to fit if necessary. Top with one-third of bolognaise sauce and one-third of remaining béchamel sauce. Repeat pasta and sauce layers twice, finish with béchamel sauce. Sprinkle with mozzarella.
5. Bake, uncovered, for 1 hour or until golden and bubbling around the edges. Serve.