Heat oven to 350℉.
Cut tops off whole heads of garlic.
Drizzle each with 1½ teaspoons olive oil.
Wrap in foil.
Bake for 1 hour, or until garlic is cooked through.
While garlic is roasting, peel and dice potatoes.
Rinse and place in a 6 quart stockpot.
Add water to about 1 inch above potatoes.
Add salt, as desired.
Bring to a boil.
Reduce heat and cook until tender, about 20 minutes.
Drain potatoes.
Use a potato ricer to crush potatoes into the stockpot, or a large bowl.
Squeeze garlic out of its skin into the potatoes.
Add sour cream.
Use a hand mixer to combine.
Season to taste with salt and pepper.