Place the garlic and potatoes in a 3-quart saucepan and cover with water; cook until fork tender and drain.
While potatoes are cooking preheat oven to 325F and lightly spray a 1 ½ quart casserole dish with cooking spray.
Add butter and sour cream to the potatoes and mash using a potato masher or electric mixer, and then fold in the chives. Spoon the mashed potatoes into the casserole dish and bake for about 20 minutes or until hot. Top with the cheese and French fried onions and continue to bake until cheese is melted.