Heat oven to 400° F. Cut garlic bulb in half; place on sheet of foil. Drizzle 1 tablespoon of the olive oil over garlic; wrap foil around and over garlic. Bake 40 minutes.
After about 15 minutes of baking, peel and cut potatoes into 1-inch chunks; place in 2-quart saucepan. Add 3/4 teaspoon salt; cover with water. Heat to boiling over high heat. Reduce heat to simmer; cook about 15 minutes or until fork tender.
In small saucepan or microwavable bowl, heat or microwave remaining 2 tablespoons olive oil and the half-and-half until warm.
Drain potatoes; return to saucepan or another bowl. Squeeze roasted garlic cloves into potatoes; mash with fork or potato masher. Add warm half-and-half mixture; mash until creamy. Season to taste with salt and pepper; garnish with basil.