1. Preheat your oven to 375°F.
2. Cook the pasta shells according to package instructions until al dente. Drain and set aside.
3. In a skillet over medium heat, warm the olive oil. Add the garlic and cook until fragrant, about 1 minute. Stir in the chopped spinach and cook until wilted, about 2-3 minutes. Remove from heat and let cool slightly.
4. In a large mixing bowl, combine ricotta, 1/2 cup of the mozzarella, Parmesan, egg, cooked spinach, Italian seasoning, salt, and pepper. Mix until well combined.
5. Spread 1 cup of marinara sauce evenly in the bottom of a 9×13 inch baking dish.
6. Spoon the ricotta mixture into each shell and place them in the prepared dish, open side up.
7. Top the shells with the remaining marinara sauce and sprinkle with the remaining mozzarella cheese.
8. Cover with foil and bake for 20 minutes. Remove the foil and bake for an additional 10 minutes, or until the cheese is bubbly and golden.
9. Garnish with fresh basil leaves if desired before serving.

Cooking is all about feeling your way through it sometimes. If the sauce bubbles too quickly, just lower the heat a bit. Trust your instincts and remember that a little imperfection is part of the charm.