Spray four cups in a muffin tin with olive oil. Place a sweet potato slice in each cup; spray top of slice lightly with more olive oil. Repeat until cups are filled and sprinkle with salt and pepper.
Bake for 30-40 minutes or until edges of potatoes become crispy.
While potatoes are baking, heat olive oil in a small skillet over medium-high heat. Add sage leaves and saute, stirring constantly, for about 3 minutes or until leaves are crispy, but still green. Divide sage leaves onto the tops of the potato stacks.