Preheat your oven to 180°C (350°F) and set a baking dish aside.
Cook the pasta in salted boiling water until just al dente, about 8 minutes. Drain and set aside.
Melt the butter in a large skillet over medium heat, then add diced onion. Sauté until translucent and fragrant, about 5 minutes, until the onion is soft and slightly golden.
Stir in the pumpkin purée and a pinch of nutmeg, then pour in the cream. Let simmer gently for about 3 minutes, stirring occasionally, until warmed through and slightly thickened.
Meanwhile, prepare the cheese sauce by gradually whisking the milk into melted butter and flour in a separate pan to create a roux. Cook until thickened and smooth, about 3-4 minutes.
Whisk the cheeses into the pumpkin mixture, stirring until melted and fully incorporated. Season with additional nutmeg if desired.
Add the cooked pasta into the cheese and pumpkin sauce, stirring gently to coat evenly. Transfer the mixture into your prepared baking dish.
In a small bowl, toss the panko breadcrumbs with olive oil. Sprinkle evenly over the top of the pasta mixture.
Bake in the preheated oven for 20-25 minutes until the top is golden brown and bubbling around the edges.
Remove from the oven and let sit for 5 minutes to set, then serve hot, enjoying the creamy pumpkin flavor with crispy topping.
