Salt both sides of your eggplant slices and place them in a large colander in the sink. Let the liquid drain for 45 minutes to 1 hour.
When your eggplant slices have finished draining liquid, brush off the excess salt, as you don't want it to be too salty!
In 2 shallow plates, add breadcrumbs to one and whisk eggs and milk in the other. Dip both sides of eggplant slice into milk/egg mixture then cover with breadcrumbs, shaking off the excess. Place on plate or large baking sheet and repeat until all eggplant slices have been coated.
Preheat oven to 375 degrees.
Heat a skillet over medium high heat and add 1 tbsp. of vegetable oil into the skillet. Once the skillet is hot, add two eggplant slices at a time to the skillet and cook on both sides until golden brown, remove and set on a large plate lined with paper towels. Repeat until you've pan-fried them all.
In a large casserole dish, add 1 cup of marinara sauce to the bottom of the casserole dish. Add a layer of eggplant slices then using a 1/4 cup, dollop marinara sauce on top of the eggplant slices. The idea isn't to smother the layers with sauce. On top of the eggplant slices, sprinkle a generous amount of mozzarella cheese and parmesan cheese. Repeat the layers until you run out of eggplants slices. Top the casserole with more cheese before you place in the oven.
Bake for 20-25 minutes, or until the cheese is bubbly and brown on top. You can use the broiler for 5 minutes to get the cheese nice and brown - you don't have to, but if you do, watch it carefully!
Serve hot and top with chopped basil, if using.