Scrub potatoes; prick each several times with a fork. Bake at 400° for 1 hour and 15 minutes or until done. Let cool slightly.
Melt margarine in a large nonstick skillet over medium-high heat. Add broccoli and onion; saute 3 minutes. Add broth; bring to a boil. Cover, reduce heat, and simmer 5 minutes or until broccoli is tender. Remove from heat; stir in ham and pepper.
Cut a lengthwise strip from top of each potato;discard strips. Scoop out pulp, leaving 1/4-inch-thick shells; set shells aside.
Place potato pulp in a bowl; add 2 tablespoons sour cream, and mash slightly. Stir in broccoli mixture. Spoon mixture evenly into potato shells.
Place potatoes in an 11- x 7- x 1 1/2-inch baking dish coated with cooking spray. Bake at 400° for 15 to 20 minutes or until thoroughly heated. Top each potato with 2 tablespoons Cheddar cheese, and bake 3 additional minutes or until cheese melts. Top each with 1 tablespoon sour cream.