Halve eggplants lengthwise. Brush cut sides with 1/4 cup oil and season with salt. Arrange as many eggplants, cut sides up, as will fit in 1 layer on rack of a broiler pan and broil 2 to 3 inches from heat until browned, about 5 minutes. Turn oven setting to 450°F. and move pan to middle of oven. Roast until tender when pierced with a fork, about 12 minutes. Repeat with remaining eggplants.
Blend remaining 1 1/2 cups oil and remaining ingredients in a blender until emulsified.
Serve eggplants at room temperature, drizzled with vinaigrette.
