In the microwave oven, cook the potatoes on maximum intensity for 8 to 10 minutes or until just tender. Let cool.
Cut each potato in half lengthwise. Remove the flesh of the potatoes, leaving a ½-cm (¼-inch) of potato on the skin. Keep the scooped potato flesh for another use. Oil the inside. Season with salt and pepper. Put the potato skins in an airtight container. Refrigerate.
Preheat half the grill, setting the burners to medium. Oil the grate.
Brown the potatoes, skin side up. Transfer to a plate. Spread the mascarpone inside the potatoes. Sprinkle with the cheddar and Parmesan cheese. Place the potatoes on the off section of the grill. Close the lid and cook for about 10 minutes or until the cheese has melted. Serve with steaks or top with Beer Chili (see recipe).
Instead of cooking the potatoes in the microwave oven you can leave them wrapped in aluminum foil in the middle of a 180 °C (350 °F) preheated oven or on the grill for about 1 hour, while tailgating.