Pre-heat the oven to 375. Line 2 large baking sheets with aluminum foil or parchment paper and lightly mist with cooking spray.
Beat the egg whites in a bowl with a whisk until well combined. In a shallow bowl or dish, combine the bread crumbs and grated Parmesan and mix together. Dip each slice of eggplant into the egg whites, coating all sides and then allow excess to drip off. Then dip the coated eggplant into the bread crumb mixture, coating all sides and transfer the breaded eggplant to the prepared baking sheet. Repeat for all eggplant slices. Spray the tops of the breaded eggplant slices with cooking spray and bake for 20 minutes. Flip the eggplant slices over, spray with cooking spray and return to the oven for another 15 minutes.
While the eggplant is baking, bring the teaspoon of olive oil over medium heat in a medium saucepan. Add the chopped onion and stir to coat. Cook, stirring occasionally, for a few minutes until onions are softened. Add the minced garlic and cook for an additional minute. Add the crushed tomatoes, tomato sauce, tomato paste, basil, Italian seasoning, salt, sugar and the bay leaf to the onion mixture and reduce heat to low to simmer. Stir to combine and let simmer for 15 minutes or until eggplant is done from step 2. Remove the bay leaf before using the sauce in the casserole.
In a mixing bowl, combine the sour cream, cream cheese and egg and mix until smooth (easiest using a hand mixer but you can do it by hand with a spoon as well.)
When the breaded eggplant is done baking, lightly mist a 9x13 casserole dish with cooking spray. Spread about 2/3 cup of the sauce across the bottom of the dish and place a single layer of the eggplant rounds on top. Drop spoonfuls of the sour cream mixture (using about half) across the eggplant layer and spread with the back of a spoon. Spread about a cup of the tomato sauce over the top of the sour cream mixture and follow it with a layer of the remaining eggplant rounds. Follow with another layer of sour cream mixture (use the rest) and another sauce layer (use all remaining sauce). Top with the shredded mozzarella and bake in the oven for 20 minutes until heated through and cheeses are melted.