Prepare the penne. Boil the penne in slightly salted water until al dente, drain and return to the pan and drizzle with olive oil. Stir the penne so that it is coated with the oil which stops it sticking together. Set to one side until the construction phase.
Prepare the spinach. Steam the spinach until wilted, squeeze out excess water and set to one side.
Finely chop the onion and slice the leek. Drizzle some olive oil into a heavy based frying pan and cook the onion and leek for about 5 to 10 minutes, till soft. Set aside.
Prepare the sauce. Empty the tins of tomatoes and creme fraiche into a large bowl and mix together and season with salt and paper.
Pre-heat the oven to 180 C / Gas 4. Grease a large casserole dish.
Line the base of the dish with the spinach then spread half of the penne on top and pour half the sauce on top of the penne. Now, add the onion and leek and then add the remaining penne. Break the mozzarella into small pieces and dot these on top of the penne. Finally, pour over the remain sauce and grate Parmesan over the top.
Bake for 30 to 40 minutes, or, until golden brown. Enjoy.