Instructions

1. Preheat oven to 400˚.
2. Rub olive oil over potatoes and lightly sprinkle with kosher salt, if desired. Place on middle rack of oven and bake 30 minutes. Prick each potato with a fork and continue cooking until potatoes are tender, about 15 additional minutes.
3. When potatoes are cool enough to handle but still warm, slice off 1/4 piece from the top of each potato and, with a melon baller or spoon, scoop flesh into a large bowl. Leave about 1/4-inch-thick shell on the potato "bowl" and place potato shells on a baking sheet.
4. Mash potato flesh with  butter (or oil), sour cream (or yogurt), half-and-half or cream (or milk), garlic and spinach. Reserve.
5. When mixture is cool, stir in desired amount of cheese, and season to taste with kosher salt and freshly ground pepper. Stuff potato mixture into potato shells and sprinkle each potato with remaining 1/4 cup cheese. (This can be done up to 24 hours in advance at this point.)
6. Bake on middle rack in 400˚ oven until heated through, 20-30 minutes.