PREPARATIONArrange one layer of eggplant on a tray or baking sheet lined with paper towels and sprinkle with some kosher salt. Turn eggplant over and salt other side. Cover eggplant with a layer of paper towels and top with another layer of eggplant, sprinkling with some kosher salt. Repeat layering with paper towels and remaining eggplant and kosher salt and let stand about 20 minutes. (Paper towels will absorb liquid from eggplant.)
On an oiled baking sheet arrange one layer of eggplant and broil about 3 inches from heat until pale golden, about 3 minutes. Using tongs or a spatula, turn eggplant over and broil until pale golden and tender, about 2 minutes more. Transfer cooked eggplant to a platter and broil remaining eggplant in same manner.
In a large non-stick skillet cook onion in 1 tablespoon oil over moderately low heat, stirring, until soft and pale golden and transfer to a bowl. Add spinach to skillet and saute over moderately high heat, tossing and turning with tongs, until wilted. Season spinach with salt and pepper and stir into onion.
In a blender puree basil, garlic, and 6 tablespoons oil until smooth. Season basil mixture with salt and pepper. Preheat oven to 450°. And generously brush a 10 by 3 inch round cake pan with some oil.
Line side and bottom of pan with a layer of eggplant. Brush eggplant with some basil mixture and spread some spinach mixture evenly over eggplant. Layer some tomato slices over spinach mixture and brush with some basil mixture. Repeat layering with remaining eggplant, basil mixture, spinach mixture and tomatoes in same manner, ending with a layer of tomatoes.
Bake eggplant tian in the middle of the oven for 20 minutes. Cool tian in pan on a rack 1 hour and invert onto a shallow serving dish.
Makes a good side dish.