Preheat the oven to 325 degrees F. Lightly butter a 1 ½ quart baking dish. Place the potatoes and garlic cloves into a 3-quart saucepan and add enough cold water to cover the potatoes and garlic. Bring to a boil. Cover, reduce heat and cook for 20 minutes or until fork tender. Drain all of the water from the potatoes and garlic.
Add the butter and sour cream to the drained potatoes and garlic and mash using a potato masher or electric mixer until mixed well. Stir in chives. Place the mashed potatoes into the casserole dish. Place into the oven and bake at 325 degrees F. for 20-25 minutes or until hot.
During the last few minutes of cooking remove the baking dish from the oven and top the mashed potatoes with the cheddar cheese and French fried onions. Return to the oven and bake until the cheese has melted.