Preheat oven to 375 degrees F. Pierce potatoes with a fork multiple times. Place directly on an oven rack and bake for 1 hour and 15 minutes, or until they’re cooked through and the inside is soft. Let cool slightly.
Meanwhile, heat the olive oil in a large sauté pan over medium heat. Add garlic and cook for 1 minute. Add the spinach and season with salt and pepper. Stir to coat with the olive oil and let cook until spinach is wilted, about 7-8 minutes. Transfer spinach to a mesh strainer, and push spinach against the strainer to squeeze out the excess liquid.
When potatoes are cool enough to touch, slice each in half lengthwise and scoop the flesh, leaving enough of a border that the potato halves hold their shape, into a large mixing bowl. Brush the inside of each emptied potato half with olive oil and sprinkle with salt and pepper. Set on a baking sheet.
Add cream cheese, butter, sour cream, ¾ of the fontina, salt, and pepper to the potatoes. Mix with a hand mixer until completely smooth. Fold in the spinach and chopped artichokes. Scoop even portions of the potato mixture into the empty potato halves. Sprinkle the tops evenly with shredded parmesan and the remaining fontina.
Bake for 30-35 minutes until cheese is melted and potatoes are heated through.