Preheat the oven to 450 degrees F. Cover the potatoes with cold water seasoned with salt and pepper. Bring the potatoes to a boil and cook until tender. Drain well.
In a medium saucepan, heat the cream and chopped sage over medium-low heat until the cream is very warm and has been infused with the sage flavor, about 5 minutes. Add the potatoes to the sage-infused cream along with the butter and Parmesan cheese. Mash the potatoes until smooth, season to taste with salt and pepper and cool until thickened, about 20 minutes.
Meanwhile, heat the olive oil in a skillet over medium-high heat. Add the whole sage leaves and fry until dark green and crisp, 30 seconds to 1 minute. Drain on a paper towel-lined plate. Place the cooled potatoes in a piping bag fitted with a large star tip. Divide and pipe into 4 equal mounds on a baking sheet and bake until golden brown, 6 to 8 minutes. Garnish each mound with a fried sage leaf.
Cook's Note: Be sure to infuse enough sage in the cream so you can taste the herb through the potatoes. The great thing is you can make these in advance and pop them in the oven when you are getting ready to eat.