Heat the oven to 325˚. Break the heads of garlic apart, then mash each clove to release the clove from its papery skin; if using already-peeled garlic, scoop the cloves into a heavy plastic bag and use a rolling pin to mash them slightly.
Stir together the garlic, oil and salt in an 8x8-inch pan (make sure all the garlic is submerged), slide it into the oven and bake until the garlic is soft and lightly brown, about 45 to 55 minutes. Add the lime juice and return to the oven for 20 minutes for the garlic to absorb the lime and turn golden brown. (If you’re using the larger quantity of oil, ladle off 1 cup—no garlic cloves—and store it in a cool dry place for use in salad dressing or sautéing.)