Wash the purple sweet potato thoroughly. Microwave for about 5-10 minutes until tender or bake at 400°F (200°C) for 40-45 minutes. Let cool, peel off the skin and mash in a large bowl until smooth.

In the bowl with the mashed sweet potato, add flour, Parmesan cheese, egg, and salt. Mix until a cohesive dough forms; add more flour if it's too sticky.

Divide the dough into four equal parts, roll each into a long rope about 1/2-inch thick, and cut into ½-inch pieces. Use a fork to create indentations on each piece.

Bring a large pot of salted water to a boil. Add gnocchi in batches and boil for 3-5 minutes or until they float. Remove with slotted spoon and drain.

In a skillet, melt butter over medium heat. Add garlic and sage, cooking until aromatic. Add boiled gnocchi and toss gently to coat in sauce.