Preheat your oven to 180°C (350°F).
Cook the pasta in a large pot of salted boiling water until just al dente, about 8 minutes, then drain and set aside.
In a saucepan, melt 1 tablespoon of butter over medium heat, then whisk in the flour and cook for about 1 minute until slightly bubbling and fragrant.
Gradually pour in the milk while whisking constantly to prevent lumps, and cook until the mixture thickens and starts to bubble, about 5 minutes.
Stir in the pumpkin puree, grated cheese, a pinch of nutmeg, and the remaining butter. Continue stirring until the cheese melts and the sauce is smooth and creamy.
Fold the cooked pasta into the cheese and pumpkin sauce until evenly coated.
Transfer the pasta mixture to a baking dish and sprinkle evenly with breadcrumbs and a little extra cheese.
Bake in the preheated oven for about 20 minutes, until bubbling around the edges and the top is golden brown.
Remove from the oven and let cool slightly before serving. Enjoy the warm, cheesy, and crispy pumpkin mac and cheese!