Preheat oven to 350F/180C.

Melt butter in a deep fry pan or skillet (Note 2) over medium heat. Add the onion and garlic and sauté for 5 minutes until translucent. Add the flour and stir to combine, then cook for 2 minutes.

Add the milk and whisk for 1 minute, in small circles around the fry pan, until it starts to thicken. Then add the tomato passata, water, salt and pepper. Increase the heat to medium high and cook for around 5 minutes or until thick enough to coat the back of a metal spoon (see photo below). Whisk occasionally for the first 3 minutes, then whisk constantly for the last 2 minutes.

Do a taste test and add 1 to 2 tsp of sugar if it is a bit sour (depends on quality of passata you use).

Add the ziti/penne, chicken and cheddar cheese and mix through. Leave it to cook for around 1 minute on the stove, then take it off the stove.

Scatter with mozzarella cheese. Cover with a lid or foil (Note 3) and bake for 10 minutes. Remove the lid/foil and bake for a further 5 minutes. Rest for 5 minutes before serving, garnished with fresh basil leaves and grated parmesan, if desired.