Preheat the oven to 400°F and prepare a baking sheet.
Rub the outside of each potato with olive oil and pierce each with a fork several times.
Place each potato on the baking sheet and bake for 50-60 minutes, or until fork-tender.
While potatoes are baking, in a medium saucepan, bring water to a boil over high heat. Reduce heat to low, add kale, cover, and cook for 2-3 minutes, until the kale turns bright green. Drain, dry well, and set aside.
Remove potatoes from the oven and let cool until you can handle them.
Cut potatoes in half lengthwise and scoop out the flesh leaving ¼ inch potato flesh on the bottom and sides of the potato skin. Set the hollowed potato skins aside.
Place potato flesh in a large mixing bowl and mash with butter, buttermilk, and sour cream until desired consistency.
Gently fold in cooked kale, Fontina cheese, green onions, salt, and pepper.
Discard a couple of the hollowed-out potato halves so you have more stuffing for the remaining skins (optional).
Scoop the mixture into the potato shells, sprinkle each with Parmesan cheese, and place on a baking sheet.
Bake at 400°F for 15-20 minutes, until golden on top.