Wash the eggplants and make a few deep cuts in the skin. Put them on a baking sheet and place in a 450F oven for about 1 hour, or until the skin is burned and crispy when you touch it. You want the skin to be burned to give the dip a smoky flavor. Allow the eggplants to cool and cut them open and scoop out the flesh. Discard the large dark seeds.
Place the flesh in a colander and salt it, and add the lemon juice. Allow the flesh to drain for about one hour. Place the drained flesh in a bowl and mash with a fork. Add the yogurt, garlic and olive oil and stir until it is smooth.