In a large pot of boiling water add the tomatoes that you will have gently scored a X on the bottom and a fine line all around the middle. Blanch for a couple of minutes until you will see the skin pulling away from the tomato meat. Drain and rinse under cold water. Remove the skin and pass the tomatoes thru a food mill or crush with a potato masher. Set aside.
In a large skillet over medium heat add the olive oil and cook the finely chopped onion until they become translucent.
Add the eggplant to the onion and cook for a couple of minutes. Add the tomato and some water (1/4 cup) to continue the cooking process. Season lightly with salt, very little.
Meanwhile, cook the pasta according to packaging instruction and drain 2 minutes prior to being al dente. Reserve cooking water.
Add the pasta to the eggplant tomato sauce and coat well with the sauce Add some of the cooking water if too dry.
Serve the pasta into a bowl and sprinkle a generous amount of ricotta salata over it.