To make the gnocchi: 

1. Preheat the oven to 350°F. Cut the sweet potatoes in half and place them cut side down on a baking sheet brushed with oil. Bake for 20 to 30 minutes, until tender.
2. Let them cool until you can handle them, then scoop the potato from the skins into a large mixing bowl.
3. Mash the potatoes with a potato masher or ricer.
4. Add the garlic, Parmesan cheese, salt, and egg and egg yolk, and stir to combine.
5. Add the flour a little at a time, mixing until the mixture forms a workable dough.
6. Take a large meatball-sized piece of dough and roll it on a floured surface into a rope about ½ inch in diameter. Cut it into ½-inch pieces. Repeat with the remaining dough.
7. Roll each piece down a fork or gnocchi rolling board while pressing in with your finger to hollow the inside. Continue until all the dough is rolled.
8. Arrange the gnocchi on a baking sheet. (To freeze, freeze them on the sheet, then transfer them to zip-top bags and freeze for up to 2 months. Cook them straight from frozen.)
9. Bring a large pot of salted water to a boil. Drop in the gnocchi and cook until they float. Remove them from the water and place in a bowl.

To make the sauce:

1. In a large sauté pan, melt the butter over medium heat, adjusting the heat as needed to brown the butter without burning it.
2. Roughly chop the sage leaves. Add them to the butter and cook for 2 to 3 minutes over low heat. Remove the crispy sage and set it aside
3. Add the gnocchi and cook until slightly browned, about 3 minutes.
4. Add the pumpkin and mix, then add the milk and mix until well combined. Season with the salt to taste.
5. Serve topped with the crispy sage.