Preheat the oven to 180°C conventional oven/ 160°C fan-forced (350° Fahrenheit/Gas 4). Grease a baking dish with butter or margarine.
Cook the broccoli in a large pot of boiling water over medium heat until very tender (approximately 20-25 minutes). Take the pot off the heat. Remove the broccoli with a slotted spoon and transfer to a blender. Roughly pulse so that the broccoli mixture is smooth with some small pieces intact. Transfer the broccoli mixture to a large bowl. Set aside the pot with broccoli infused water.
To make the Besciamella sauce, melt the butter in a medium-sized saucepan over medium heat until foaming. Add the flour and stir with a wooden spoon to form a smooth paste (a roux). Allow the flour and butter mixture to cook for a minute (but do not allow it to brown). Remove from the heat. Slowly pour the cold milk into the roux, stirring constantly, until the mixture is smooth. Add the bay leaf and return to medium heat. Cook, stirring with the wooden spoon until the Besciamella comes to the boil and thickens (approximately 10 minutes). Remove from heat. Season with salt to taste and stir in freshly grated nutmeg. Set aside to cool slightly.
Place the pot with broccoli infused water on high heat and bring to the boil (add more water, if required). Add a pinch of salt and mezzi rigatoni pasta to the boiling water and cook for ¾ of the ‘al dente’ cooking time – refer to the cooking time specified in pasta packet instructions. Drain the pasta, then add to the bowl with broccoli. Toss to combine.
Meanwhile heat the olive oil in a large frying pan over medium heat. Add the garlic and chilli. Cook for 2 minutes or until aromatic. Break up the sausage meat with your hands and add it to the frying pan. Cook, stirring with a wooden spoon, breaking up any lumps until the sausage meat is lightly browned all over. Stir in the broccoli mixture until combined. Cook over the heat for 2 minutes. Season to taste, then remove from the heat.
Spread 1/4 of the Besciamella sauce over the base of the baking dish. Set aside 1/4 of the Besciamella sauce (for the last layer of the pasta al forno (pasta bake). Add the remaining Besciamella sauce to the broccoli pasta mixture. Toss to combine. Ladle 1/2 of the creamy broccoli pasta over the Besciamella layer, using the back of a ladle to press it down and level it. Add a layer using 1/2 of the Provolone cheese cubes. Sprinkle 1/3 of the Parmigiano Reggiano cheese on top of the Provolone. Continue layering using the remaining creamy broccoli pasta (once again pressing it down with a ladle) and Provolone cheese. Finish with a layer of Besciamella sauce and remaining Parmigiano Reggiano sprinkled to cover the Creamy broccoli and pork sausage pasta al forno (pasta bake) and a few knobs of butter (or margarine) on top.
Bake in a preheated oven for 25 minutes. Change to the grill setting of the oven (same oven temperature). Brown under the grill for 5 minutes or until lightly golden on top. Remove from the oven and allow to rest for a minimum of 10 minutes before serving.
Cut the Pasta al forno into 6 portions and serve – buon appetito.