• Pre-heat the oven to 180 C / 350 F.

To make the Ragu

• Heat the olive oil in a pan over a medium heat. Add the onions and cook until softened - approximately 10 minutes.
• Add the garlic and continue to cook for 2 minutes.
• Stir in the can of tomatoes, chicken stock and herbs. Season with salt & pepper and mix together.
• Bring to the boil and let it cook & bubble for a good 20 minutes, stirring occasionally. You want to end up with a good thick sauce.
• Stir in the chicken and heat through for around 5-10 minutes.
• Meanwhile, make the cheese sauce

To make the Cheese Sauce

• Melt the butter in a saucepan over a medium heat.
• Stir in the flour and use a whisk (or wooden spoon, but whisk is easier) to stir the flour into the butter to make a paste. Continue to stir for a minute or so.
• Gradually add in the milk, stirring all the time.
• Continue stirring over a medium heat until the mixture has thickened to sauce consistency.
• Stir in the grated cheese and continue stirring until the cheese has all been incorporated and you have a thick, creamy sauce.

To assemble the Lasagna

• Line the lasagna dish with a thin layer of ragu.
• Place the lasagna sheets on top.
• Pour over a thin layer of cheese sauce, followed by another thin layer of ragu, then another layer of lasagna sheets.
• Continue layering in this order until you have used up all your ragu and cheese sauce. It doesn't matter if you finish off with a layer of ragu or cheese sauce.
• Sprinkle the grated cheese over the top
• Bake in the oven for 25 minutes. It should be golden brown and bubbling.