Clean potatoes. Pierce each potato several times with fork. Microwave on high for about 10 minutes; rotate potatoes. Microwave until tender, about 3 more minutes.

Preheat oven to 350 °. Cut Melt butter in medium pan over low heat. Add onion; cook until clear, about 5 minutes. Slice off tops of potatoes.

Scoop out potatoes, keeping shells intact; place pulp in a bowl. Mash pulp and add onion, 1/2 cup cheese, sour cream, chives, salt and pepper.

Spoon mix into shells; cover with remaining cheese and bake until hot, about 10 minutes.