Preheat the oven to 180°C (350°F) and lightly grease a medium baking dish.
Cook the macaroni in salted boiling water until just al dente, then drain and set aside.
Melt butter in a saucepan over medium heat, whisk in flour, and cook for 1 minute to form a roux.
Gradually add milk while whisking until the sauce thickens and becomes smooth.
Stir in pumpkin purée, followed by grated cheeses, until melted and creamy.
Season with salt, pepper, and nutmeg, then fold in the cooked macaroni to coat thoroughly.
Pour mixture into the prepared dish, top with breadcrumbs and small bits of butter.
Bake for 20–25 minutes until bubbly and golden brown. Garnish with crispy sage before serving.