Place potatoes in a medium pot, cover with 1 inch of water, and bring to a boil. Reduce heat, simmer for 20-30 minutes until easily pierced with a fork. Drain, reserving ¼ cup starchy water, and let cool to room temperature.
Mash potatoes finely using a potato masher. Measure ¾ cup packed potatoes, saving the rest for later.
On a clean surface, mix mashed potatoes with all-purpose flour, pumpkin, and salt. Knead until a soft, slightly sticky dough forms. Add flour or reserved starchy water as needed.
Once smooth, knead dough briefly. Shape into a ½ to 1-inch tall rectangle, cut horizontally into slices, roll each into a ½" diameter rope, and cut into gnocchi. You can also shape the gnocchi into pumpkin shapes using a knife if desired.
Bring a large pot of salted water to a boil. When the pot of water boils, add gnocchi and stir to prevent sticking. Boil until they float, then let sit for 30 seconds. Using a slotted spoon, transfer cooked gnocchi to the skillet and crisp in the sauce for a few minutes.
In a medium skillet over medium heat, melt butter. Add onion, cook until translucent, then add garlic and cook for 2-3 minutes. Add milk, cooking cream, Parmesan cheese, salt, pumpkin purée, and black pepper and let it cook.
Place the pumpkin gnocchi into the sauce and serve!
