Step 1

Prepare the grill for indirect heat: If using a gas grill, preheat to medium-high (400 degrees) for 10 minutes with the lid closed. If using a charcoal grill, light the charcoal or wood briquettes; when the briquettes are ready, distribute them on one side of the cooking area. For a hot fire, you should be able to hold your hand about 6 inches above the coals for 3 or 4 seconds. Have ready a spray water bottle for taming any flames. Brush the grill grate.

Step 2

Scrub the potatoes and wrap each one in aluminum foil. Arrange them on the indirect-heat side of the grill. Close the lid and cook for about 1 hour and 30 minutes, until tender. Transfer to a plate to cool (still wrapped) for 10 minutes.

Step 3

Meanwhile, cut the bell peppers in half from top to bottom (through or beside each stem, to preserve them). Discard the ribs and seeds.Trim a little off the underside of each bell pepper half to help it sit evenly.

Step 4

Unwrap the potatoes and scoop the flesh into a mixing bowl. Discard the skins. Add the sour cream, milk, butter, shredded cheeses, whites of the scallions, salt and pepper; mash and blend well.

Step 5

Fill each bell pepper half with the potato mixture. Arrange the stuffed pepper halves on the indirect-heat side of the grill. Close the lid and cook for 10 to 15 minutes or until the peppers just start to blister but have not collapsed. The stuffing will be browned.

Step 6

Transfer to a platter; garnish each one with the scallion greens. Serve warm.