Position oven rack in the center of the oven. Preheat oven to 425°Fahrenheit. Line a baking sheet with foil. Use a fork to prick holes in the potatoes in a few places. Bake 30 minutes, turn and bake about 30 more minutes, until tender when pierced with a fork in the middle. Allow to cool slightly and cut in half lengthwise.

When potatoes are almost done cooking, heat olive oil in a small skillet over medium heat. Add sage leaves and cook until crisp but still green, about two minutes. Transfer leaves to a paper towel to cool and reserve the olive oil in the pan. Set aside to cool for a few minutes and add the butter. It will melt in the warm oil.

Scoop most of the flesh out of the sweet potato halves and transfer to a mixing bowl. Mix in the oil with butter and cheese, crumble the sage leaves in. Taste and season with salt if desired. Transfer flesh back to the skins and return to oven to cook about ten more minutes, until skins are golden brown.