Preheat the oven to 325 degrees F. Line a baking sheet with parchment paper or aluminum foil.
Cut the top quarter from each head of garlic and place, cut side up, on the prepared baking sheet. Drizzle the oil lightly over the cut garlic tops, and sprinkle with the salt and pepper. Turn the garlic cut side down, and roast until the cloves are soft and golden brown, about 1 hour.
Remove from the oven and let sit until cool enough to handle. Squeeze each head of garlic, gently pressing with your fingers to expel the cloves into a bowl. Stir the garlic with a rubber spatula to blend thoroughly. Use as needed, or store refrigerated in an airtight container.
Yield: about 1/2 cup