Preheat the oven to 180 degrees Celsius.
Chop the pumpkin into small, bite sized cubes. Space it evenly on a baking tray, spray with olive oil, and cook for around 20 minutes, or until it is just cooked through but still firm. It will continue to cook in the pasta bake.
While the pumpkin is cooking, place a large pot of salted water over a high heat, and bring to the boil. Add the pasta, and just cook until al dente, as per the packet instructions. The pasta will continue to cook in the bake, so make sure it isn’t mushy and overcooked. Turn the heat off, drain the pasta and return it to the pot, reserving a little starch water to keep the pasta from sticking together while you assemble the dish.
Grate the cheeses and measure out the ingredients for the white sauce. If you like a saucier pasta, use the higher amount of milk – 3 cups if you’re not using white wine, 2-1/2 if you are using white wine. If you like a thicker sauce, use less liquid – 2 1/2 cups of milk if you are not using white wine, or 2 cups of milk and 1/2 cup of white wine if you are.
Add the butter to a medium saucepan over a medium heat, and allow it to melt. You can use olive oil as a substitute, if you prefer. Once melted and/or warm, add the corn flour, and whisk to combine. Add the liquids, and continue whisking over the medium heat until the sauce thickens. This could take anywhere from 5-10 minutes, depending on the volume of liquid you are using.
Once the sauce has thickened, add the cheeses, ditch the whisk, and stir well to combine. When they have melted, add the nutmeg, pepper, and salt to taste.
Add the white sauce to the pasta, and stir well to combine. Once the pasta is coated, add the pumpkin and herbs, and gently stir them through.
Turn the oven to the grill setting. Transfer the pasta into the Lodge cast iron pot, and top with the remaining halloumi. Give the top a spray with olive oil, and cook the bake for 20 minutes, or until golden brown and crispy on top. Top with herbs and serve immediately.