Cut off pointed end of garlic; place garlic on a piece of aluminum foil, and drizzle with 1 tablespoon oil. Fold foil to seal. Brush corn with 1 tablespoon oil and place on a baking sheet.
Bake garlic at 400 degrees for 1 hour. After 15 minutes, place corn in oven, and bake, with garlic, 45 more minutes or until corn is golden brown. Squeeze pulp from garlic cloves, and set aside. Let corn cool completely.
Hold 1 corncob upright on a cutting board and carefully cut downward, cutting kernels from cob. Repeat with remaining 2 corncobs. Discard cobs. Set corn aside.
Cook potatoes in boiling water to cover in a large saucepan until fork-tender (about 15 to 20 minutes). Drain and return to pan.
Whisk together reserved roasted garlic pulp, 3/4 cup sour cream, 1/2 cup butter and next 5 ingredients in a medium saucepan over medium heat until butter melts and mixture is thoroughly heated. Do not boil.
Mash potatoes slightly; add warm garlic mixture to pan and continue to mash just until blended (mixture should be coarsely mashed). Stir in chopped cilantro and reserved corn.