Double Stuffed Potatoes

4 large baking potatoes
2 Tbsp butter or margarine
1/2 C chopped onion
3/4 C shredded cheddar cheese, divided
1/4 C sour cream
2 tsp dried chives
salt and pepper

Scrub potatoes; pat dry. Pierce potato several times with a fork. Microwave on HIGH 10 minutes; rotate potatoes. Microwave until tender, about 3 minutes longer. Preheat oven to 350. Melt butter in skillet over low heat. Add onion; cook until translucent, about 5 minutes. Slice off potato tops. Scoop out potatoes, keeping shells intact; place pulp in medium bowl. Mash potato pulp; add onion, 1/2 cup cheddar, sour cream, chives, salt and pepper. Spoon potato mixture into shells, dividing evenly. Sprinkle potatoes with remaining cheddar. Place in medium casserole. Bake potatoes, until heated through, about 10 minutes.