Preheat oven to 400 degrees (F). Remove excess papery skins from garlic bulbs and carefully slice off the top of the bulbs; place in a small oven-safe baking dish, drizzle with 3 teaspoons of olive oil. and wrap the bowl in heavy-duty foil. Bake for 40 minutes, or until the inner garlic cloves have softened. Set aside to cool.

Meanwhile, in a large skillet over medium-low heat, saute the onions in remaining 3 tablespoons of olive oil, stirring occasionally, for 25-30 minutes, or until golden brown. Transfer to a food processor or strong blender, cover, and process until blended; set aside.

Place potatoes in a large stockpot and cover with water; bring to a boil over high heat. Once at a rapid boil, reduce heat to medium-low, cover, and cook for 15 minutes, or until tender enough to pierce with a fork. Drain the potatoes well. Place potatoes in a large bowl; add in the roasted garlic cloves, butter, sour cream, cheese, heavy cream, salt, pepper and onion mix. Using a handheld electric mixer on low-speed, beat potatoes until light and fluffy. Taste and adjust salt and pepper as needed. Serve warm.