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.