To make the bechamel, heat the milk in a saucepan until just warm and set aside. In a large casserole, melt the butter over a medium heat until foamy, quickly add the flour and whisk until a smooth roux is formed. Reduce the heat to low and whisk for 2-3 minutes to cook out the raw flour. While continuing to whisk, slowly add the warm milk in a steady stream and continue to whisk until the sauce is thickened and smooth. Add the grated cheddar and season and to taste. Set aside and place cling film on the surface of the sauce as to not form a skin. Boil a large casserole of salted water and cook the pasta for 10 minutes. Drain, rinse, and set aside (pasta water should always be well seasoned).

Preheat the oven to 180℃. To make the filling, place the spinach in a large bowl and pour boiling water over. Allow to sit for 1 minute then strain and rinse. Squeeze out as much water as you can and dry the spinach with kitchen towel. Finely chop the spinach and place in a large bowl with the remaining stuffing ingredients and season well. Place the stuffing in a piping bag and set aside. Remove the plastic from your bechamel and warm slightly over a low heat whisking while you do so. Pour the warm bechamel into a Le Creuset 33cm Heritage Rectangular Dish with Lid and spread out evenly. You may not need all the bechamel, simply freeze any remaining bechamel for your next pasta. Nestle the pasta shells in the sauce and once the entire surface is covered, stuff each shell with the ricotta spinach stuffing. Sprinkle over grated Parmesan cheese if you like and bake for 40-50 minutes until golden and bubbly. Serve immediately.