Heat oil in a large heavy based pot over medium heat. Add garlic, onion, celery and carrots. Cook for 10 minutes until softened and sweet - they should not brown (if they do, turn heat down).
Add beef, turn heat up and cook the beef, breaking it up as you go.
Once the beef has all turned brown, add the remaining Ragu ingredients EXCEPT the sugar.
Stir then adjust the heat so it is bubbling very gently. Place the lid on and cook for 1.5 - 2 hours, stirring every now and then, then remove the lid and simmer for 30 minutes.
The ragu is ready when the meat is really tender and the sauce has thickened and is rich. Adjust salt and pepper to taste, and add sugar if required.
Warm milk up in a saucepan (optional).
In a large saucepan, melt butter over medium low heat. Add flour and mix constantly for 1 minute.
Pour about 1 cup of the milk in, mixing as you go to incorporate into the flour mixture. Once mostly lump free, add remaining milk.
Turn heat up to medium high. Stir occasionally at first then regularly after a few minutes until sauce thickens - about 5 - 8 minutes.
Remove from heat, add cheese, nutmeg, salt and pepper. Mix until the cheese is melted.
Preheat oven to 180°C/350°F.
Use a 33 x 22 x 7 cm / 13 x 9 x 2.5" baking dish.
Smear a bit of Ragu on the base, then cover with lasagna sheets. Tear sheets to fit.
Spread over 2 ½ cups of Ragu, then drizzle over 1 cup of Cheese Sauce.
Top with lasagna sheets. Spread with another 2 ½ cups of Ragu, then 1 cup of Cheese Sauce.
Top with lasagna sheets then repeat 1 more time.
Top with a 4th layer of lasagna sheets, then pour over the remaining Cheese Sauce.
Sprinkle with Mozzarella, then bake for 25 minutes or until golden and bubbling.
Stand for 5 to 10 minutes before cutting and serving, garnished with basil or parsley if desired.
