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 cauliflower 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 cauliflower with a slotted spoon and transfer to a blender. Roughly pulse so that the cauliflower mixture is smooth with some small pieces intact. Transfer the cauliflower mixture to a large bowl and season with salt. Set aside the pot with cauliflower 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.
Meanwhile place the pot with cauliflower infused water on high heat and bring to the boil (add more water, if required). Add a pinch of salt and cavatappi 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 cauliflower. Toss to combine.
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 cauliflower and cavatappi pasta mixture. Toss to combine. Ladle 1/2 of the creamy cauliflower 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 cauliflower 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 cauliflower 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.