Preheat your oven to 375°F (190°C).

Boil the 18-20 jumbo pasta shells in salted water for about 1 minute less than the al dente time indicated on the package, approximately 13 minutes. Drain and rinse the shells gently with cold water to prevent sticking, then set aside.

Heat 1-2 tablespoons of olive oil in a large skillet over medium heat. Add the 3 cloves of minced garlic and cook for 1 minute until fragrant.

Add the 4 cups of fresh spinach to the skillet and toss to coat in the oil. Cook for about 3 minutes until the spinach is wilted. Set aside to cool slightly.

Combine the 15 oz ricotta cheese, 1/2 teaspoon salt, 1/4 teaspoon pepper, 1/2 teaspoon dried basil, 1/2 teaspoon dried parsley, and 1/2 teaspoon dried oregano in a large mixing bowl.

Add half of the 3 cups of shredded mozzarella cheese, most of the 1/2 cup grated Parmesan cheese (reserving some for topping), 2 tablespoons cream cheese, and 1 large egg to the bowl. Stir thoroughly to combine all ingredients.

Fold the cooled spinach and garlic mixture into the cheese filling until evenly distributed.

Spread half of the 24 oz marinara sauce on the bottom of a 9 x 13-inch casserole dish.

Fill each pasta shell with the cheese mixture using a spoon, then arrange the stuffed shells in a single layer in the prepared baking dish.

Pour the remaining marinara sauce evenly over the stuffed shells. Sprinkle with the remaining shredded mozzarella cheese and the reserved grated Parmesan cheese.

Cover the baking dish with foil and bake for 20 minutes.

Remove the foil and bake for an additional 10 minutes, or until the cheese is melted and lightly golden.

Garnish with fresh parsley before serving warm.