Peel and dice the pumpkin and potato into cubes. Boil them in a saucepan until tender, about 10-15 minutes. Drain well, then mash until completely smooth and free of lumps.
Stir in the salt and gradually add enough flour to form a soft dough. The amount of flour may vary depending on the moisture content of the vegetables. Handle the dough gently and stop adding flour once it holds together without being dry. Test-cook a few pieces to check the consistency of the dough and adjust if needed.
Lightly flour a surface or board. Divide the dough into four portions and roll each into logs about 2 cm (¾ inch) thick. Cut the logs into pillow-shaped pieces. If desired, roll each piece lightly over the back of a fork or use a gnocchi board to create ridges.
Bring a large pot of salted water to a boil. Add the gnocchi in batches and cook until they float to the surface. Remove with a slotted spoon and set aside.
For the sage butter, melt the vegan butter in a small saucepan over medium heat. Add the sage leaves and cook for 3-5 minutes until the butter is infused and the sage leaves turn crispy.
Serve the gnocchi in portions, drizzled with the sage butter and garnished with the crispy sage leaves.