Make the crespelles first (use the linked crespelle recipe) and have them ready to fill.
Preheat the oven to 375°F (190°C).
In a large bowl, stir together 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 until evenly combined.
Spoon about 1/4 cup of the spinach-ricotta filling onto each crespelle and roll up carefully.
Pour 1 cup of the marinara sauce into the bottom of a large baking dish (or divide between two smaller dishes).
Place the rolled manicotti seam-side down in the dish in a single layer.
Spoon 1 1/2 cups more marinara sauce over the manicotti, then sprinkle the reserved 1/2 cup shredded mozzarella evenly on top.
Cover the dish with foil and bake for about 25 minutes, until hot, bubbling, and the cheese is melted.