Scrub potatoes thoroughly with a clean scrubber or vegetable brush and just a little dish soap. Rinse well and pat dry with paper towels. Use the tines of a fork or the tip of a sharp knife to prick the potatoes. (Note: Piercing the potatoes prevents the potato from exploding in the oven and making a mess when the potatoes get hot and give off steam.)
Place the potatoes directly on the oven rack in the center of the oven. Bake potatoes in a 425 degree F oven for 40 to 60 minutes or till tender and potatoes yield under gentle pressure. Remove from the oven; let stand about 10 minutes or until cool enough to handle.
Sit each potato on its side. Use the tip of a sharp knife to make a small incision. Use incision to get knife started to cut potato in half vertically. (Note: This technique allows the potato to sit upright when halved.) Using a spoon, gently scoop out the flaky cooked potato pulp, leaving a 1/4-inch shell. Add the pulp to a large bowl. Use a potato masher to begin mashing the potatoes. (Note: Do not use an electric mixer or food processor for mashing potatoes. This will liquefy them, resulting in a glue-like consistency.) Add butter, sour cream, garlic, salt and black pepper. Continue mashing until desired consistency. (Note: It's best to work the potatoes as little as possible. Chunky with lumps or no lumps but do not over process or overwork them.) Taste for seasoning. (Note: At this point, you can add more butter or sour cream if you want them smoother.) Stir in the cheese and 1/4 cup snipped fresh chives.
Spoon mashed potato mixture into the potato shells. Place shells in a shallow baking pan, 13x9x2-inch baking dish or on a cookie sheet. Bake in a 425 degree F oven for 20 to 25 minutes or until lightly browned. (Note: If timing this side dish to serve with the roasted chicken dinner, cover and chill the potatoes in the refrigerator while the chicken bakes. Place potatoes in a shallow baking pan, 3-quart rectangular baking dish or on a cookie sheet. Put in the oven with the chicken for the last 20 minutes of roasting chicken. When the chicken comes out, and the temperature is increased for the asparagus, leave the potatoes in the oven. At this point, they will get golden brown and beautiful. No need to worry about doneness. As long as they are hot, they are done.)
If you like, sprinkle with additional snipped fresh chives or thinly sliced green onion and sprinkle with paprika. Makes 12 potato shells.