Preheat the oven to 350 degrees F. Lightly grease a 2-quart casserole dish with 1 teaspoon of olive oil.
Bring a medium pot of water to a boil. Add 1 teaspoon of the salt and the pasta shells, and cook until al dente, 10 to 12 minutes, stirring occasionally with a long-handled spoon to prevent the shells from sticking together. Drain and rinse under cold running water. Transfer shells to an oiled baking sheet and cover with plastic wrap until ready to use.
In a medium skillet, heat the remaining tablespoon of olive oil over medium heat. Add the onions and garlic and cook, stirring, until very soft, 6 to 7 minutes. Add the sausage and cook, stirring, until browned. Add the squeezed spinach and cook, stirring, for 3 minutes. Remove from the heat and season with salt and pepper.
In a large bowl, combine the ricotta cheese, eggs, Parmesan cheese, and 1 cup of the mozzarella cheese. Add the spinach mixture, the extra-virgin olive oil, Essence, remaining teaspoon of salt, the basil, oregano, and pepper, and stir to combine thoroughly. Spoon about 2 tablespoons of the spinach-ricotta filling into each cooked pasta shell. Place the filled shells in the prepared dish.
Pour the tomato sauce over the filled shells and top with the remaining 1 cup of mozzarella cheese. Bake, uncovered, until bubbly, about 20 to 25 minutes. Remove from the oven and let rest for 5 minutes before serving.
Adapted from "New New Orleans Cooking" by Emeril Lagasse and Jessie Tirsch © William and Morrow 1993. Provided courtesy of Emeril Lagasse. All rights reserved.