Step 1. Preheat the oven to 400°F (200°C). Place the whole eggplants on a cookie sheet and roast for 1 hour, until softened and the skins are charred.

Step 2. Carefully peel off the skins and transfer the eggplants to a glass bowl to drain. For best results, place them in a plastic colander set over a bowl and let drain overnight. (Avoid stainless steel, as it will discolor the eggplant.)

Step 3. Once fully drained, press out any remaining liquid. Transfer the eggplants to a food processor and pulse for about 30 seconds, or until finely chopped.

Step 4. Add the shredded onion, salt, and mayonnaise. Mix until smooth and creamy.

Step 5. Chill and serve cold, spread over fresh bread, with crackers, or as a flavorful side dish to any meal.