Slice just the top off of each garlic head, exposing the cloves like honeycomb (save any large chunks sliced off). Peel away any loose outer skins from the garlic heads, being careful to leave the cloves intact. Peel away and discard any cloves that look rotten. Place the little bits and cut-side-up heads in a small baking dish. Drizzle evenly with the olive oil and use your hands to coat evenly, then sprinkle with the salt. Cover the baking dish with aluminum foil and tightly seal it on two sides.
Bake for about 75 minutes, until the cloves are golden brown and easily pierced with a fork. Let cool for at least 15 minutes, then squeeze the cloves out of their paper skins.
Notes
Whole roasted garlic lasts in the fridge for 3 to 4 days, or tightly sealed in the freezer for at least 3 months with no loss of quality.