Add olive oil to a large skillet over medium heat. Add the whole eggplants, tomatoes, and peeled garlic cloves to the pan. Cover the skillet and steam and simmer vegetables for 15 minutes.
Remove the cover, turn the vegetables, drizzle with a little more olive oil, cover, and let steam for another 15 minutes. Repeat until the skin on the eggplant and tomatoes shrivels enough that you can use tongs to remove it from each. A lot of liquid will be released from the vegetables.
Once all the skin is removed and the vegetables are very soft, season the vegetables with the Kosher salt, black pepper, and red chili pepper flakes (optional). Gently press the vegetables with a potato masher, then let them simmer for another 5 minutes.
Working in two batches, use a large spoon to place ½ the mixture into a blender, liquid and all. *Making sure the top of the blender is slightly ajar, blend the mixture until smooth.
Repeat with the remaining mixture, then return to the skillet over medium-low heat; season the sauce to taste and allow to simmer for 10 minutes.
If desired, turn the heat off on the skillet and add the heavy cream. Stir to combine, then serve over your favorite cooked pasta and top with grated cheese, fresh basil, and red pepper flakes, if desired.