Scrub the sweet potatoes, wrapping individually in foil while still damp.
Place directly on the oven rack and roast for about 1 hour, until they're soft to the touch. Cool slightly before removing the foil.
While still warm, hold over a bowl and let the skins slide off, letting the flesh drop into the bowl. Discard the skin and mash the flesh along with the olive oil and cheese, seasoning to taste with the salt and pepper.
Pile the fluffy mass into a hot serving bowl and garnish with a sprinkling of Parmesan Cheese.