Cut sweet potato into spaghetti-like ribbons with a spiralizer.
Heat olive oil in a large nonstick skillet over medium heat. Add sweet potato ribbons; cook, stirring often and adding more oil to prevent sticking, until starting to soften, 6 to 7 minutes. Transfer to a plate.
Heat butter in the same skillet until melted and foaming, about 1 minute. Add sage leaves; swirl until butter is a rich caramel color and leaves are crisp and dark green, 2 to 3 minutes. Remove sage leaves from the butter. Add sweet potato; stir to coat well.
Season sweet potato with salt and garnish with crisp sage leaves.