Bring a large pot of salted water to a rolling boil and add your pasta. Cook it according to the package directions until it's al dente, since it will finish cooking briefly in the sauce later. Before draining, scoop out about a cup of the starchy pasta water and set it aside, it's a great tool for loosening the sauce later.
While the pasta cooks, heat olive oil in a large skillet over medium heat. Add the diced onion and cook until it turns soft and translucent, about 4 to 5 minutes. Stir in the minced garlic and cook for another minute, just until fragrant, being careful not to let it brown or turn bitter.
Add the pumpkin puree and vegetable broth to the skillet, stirring until everything is smoothly combined. Let it simmer gently for a couple of minutes so the flavors meld together. Stir in the heavy cream, nutmeg, salt, and pepper, and keep the heat low so the cream doesn't split.
Add the drained pasta directly into the skillet with the pumpkin sauce, tossing everything together until each piece is coated. Stir in the grated Parmesan cheese and let it melt into the sauce. If the mixture looks too thick, splash in a little reserved pasta water until it's glossy and pourable.
In a small skillet, melt the butter over medium heat and add the panko breadcrumbs. Toast them, stirring frequently, until they turn golden brown and smell nutty, which usually takes about 3 minutes. Keep a close eye on them since breadcrumbs can burn quickly once they start browning.
Plate the pasta while it's warm and generously sprinkle the toasted garlic breadcrumbs over the top. Finish with extra Parmesan cheese and a crack of black pepper for good measure. Serve immediately so the breadcrumbs stay crisp against the creamy sauce.