Preheat your oven to 200°C/ 400°F. If you don't have a cast iron casserole that can go from stove top to the oven, butter the bottom and sides of a 9 x 9 or deep 9 x 6 oven proof dish, and set aside.
Bring a large pot of water to boiling over high heat, and cook pasta until just barely tender. Drain and set aside.
While the pasta is cooking, heat the milk, butter, flour, and bay leaf over medium-high heat in medium-sized heavy-bottomed sauce pot.
Once the milk comes to a boil, reduce the heat to low, and simmer until the sauce has begun to thicken stirring frequently with a whisk, careful to not burn the milk.
Once the sauce has thickened (it should coat the back of a spoon), remove the bay leaf, and using a whisk to combine, melt in the grated cheese.
Add the pumpkin puree, smoked paprika, and salt and pepper to taste. Stir until smooth.
Combine the cooked pasta and the sauce, and spoon into the prepared dish.
In a small bowl, combine bread crumbs, grated Parmesan cheese, and olive oil. Sprinkle the bread crumb topping over the pasta, and toss into the oven.
Bake, uncovered, for 20 - 30 minutes until the top is browned and crispy, and the sauce is bubbling up the sides.
Let stand for 5 minutes prior to serving.