1. Heat your oven to 190C/Gas Mark 5.
2. Heat the oil in a large frying pan and cook the onion and garlic with a little salt for 2-3 minutes or until soft. Remove from the pan and leave to one side.
3. Turn up the heat on the same pan and fry the mince with some salt and pepper. Leave it to brown before stirring so it has plenty of flavoursome crispy bits. Once cooked, return the onion and garlic to the pan along with the herbs. Fry together for a minute.
4. Add the tomatoes, then fill the empty can with water and add half. Bring to the boil. Once it is simmering, stir in the tomato puree, the crumbled stock cube and the sugar. Leave to simmer for 20-25 minutes, or until you have a thick sauce. Add further seasoning if required and more water if it starting to get too thick or dry.
5. While you are waiting for the sauce, make the béchamel by melting the butter in a large saucepan until it is bubbling. Whisk in the flour and heat through for a minute or two, continuing to whisk so it doesn’t stick.
6. Pour in the milk bit by bit and whisk until you have a thick white sauce. Remove from the heat.
7. Stir in half the mozzarella, the nutmeg, mustard, parmesan and some seasoning.
8. Once the tomato and beef sauce is ready, add a thin layer to the bottom of a baking dish. Cover with a layer of lasagne then repeat, but this time with a drizzle of the béchamel sauce too. Repeat this process until you have used up the tomato and beef sauce and it is covered with a layer of lasagne sheets on top. Cover this with the remaining béchamel sauce (you should have half-two thirds left) and then then the remaining mozzarella.
9. Bake in the oven for about 25 minutes, or until the lasagne sheets are cooked through and it is brown and bubbling on top. Serve with a side salad.