Roast the eggplant over high heat on a grill, turning frequently on all sides, until soft and fully collapsed, about 20–30 minutes. If you don’t have a grill, you can cook the eggplants on a gas stovetop or in the oven. To use a stovetop, prick several holes in the eggplants, place them directly over a high flame, and turn occasionally with tongs or a fork until the skin is charred and the flesh is very soft. To roast in the oven, prick the eggplants and place them on a sheet pan in a 450°F oven. Roast for 50 minutes to 1 hour, flipping halfway through, until completely tender.