Prepare the crespelles according to the referenced recipe and let them cool enough to handle.
Preheat the oven to 375°F (190°C).
In a large bowl, combine the ricotta, 1 1/2 cups of the shredded mozzarella, the egg, squeezed spinach, grated Parmesan, 1/2 teaspoon kosher salt, and black pepper to taste; mix until evenly combined.
Spoon about 1/4 cup of the spinach-ricotta filling onto each crespelle, then roll up each crespelle to enclose the filling and place seam-side down.
Pour 1 cup of marinara sauce into the bottom of a large baking dish (or divide between two smaller dishes). Arrange the rolled manicotti seam-side down in the dish.
Spoon about 1 1/2 cups more sauce evenly over the manicotti, then sprinkle the remaining mozzarella on top (reserve noted earlier has been accounted for by using 1 1/2 cups then remaining).
Cover the dish with foil and bake for about 25 minutes, until the sauce is hot and bubbling and the cheese is melted.