Line a baking dish or rimmed baking sheet with foil. Scrub the sweet potatoes. Place a sweet potato on a cutting board and place a wooden spoon on each side so the potato is surrounded by the spoon handles. With a large, sharp knife, carefully cut the potatoes, making the slices about 1/8 to 1/4-inch apart. Make sure to cut straight down, and keep the potato within the spoon handles. Repeat with the remaining potatoes.
Arrange the sweet potatoes in the prepared baking pan and rub them all over with about with the blood orange olive oil. Sprinkle them with the pumpkin pie spice, a little kosher salt and freshly ground black pepper. Make sure you get the oil and seasoning between the slices.
Bake the sweet potatoes for for 40-60 minutes or until they are tender.
While potatoes are baking, prepare the sage & browned butter sauce. Slice butter and place into small saucepan and heat on medium. When butter begins to bubble, add chopped sage leaves and continue to cook for 5 minutes. Do not stir. Butter should begin foaming and the butter should be turning brown. Once it's deep golden brown and most of the foam is gone, turn off heat. Sage leaves should be crispy but not burnt. Transfer sauce to heat-proof bowl to keep the butter from continuing to cook.
Remove the sweet potatoes from the oven and drizzle them with maple vinegar then spoon browned butter and sage leaves into the sliced pieces of each potato. Serve immediately.