Preheat your oven to a temperature of 375°F.

Boil the pasta shells in salted water for approximately 12 minutes, cooking until just under al dente, then drain and immerse them in cold water to halt the cooking process; set aside.

In a skillet, warm the olive oil over medium heat, sauté the minced garlic for a minute, then add the spinach, stirring until it wilts within roughly 3 minutes; allow the mixture to cool slightly afterward.

In a large mixing bowl, combine ricotta, seasonings including salt, pepper, dried basil, and dried parsley, along with half of your mozzarella and most of the Parmesan cheese (remember to keep some Parmesan aside for topping!), then add the cream cheese and egg, mixing thoroughly; gently incorporate the cooled spinach and garlic into this mixture.

Spread a layer of marinara sauce at the base of a casserole dish, then fill each pasta shell generously with the cheese mixture using a spoon and arrange them inside the dish.

Pour the remaining marinara sauce over the shells, followed by a sprinkle of the leftover mozzarella and Parmesan cheese.

Cover the dish and bake for 20 minutes; uncover and continue to bake an additional 10 minutes, finishing by garnishing with fresh parsley before serving, accompanied by garlic bread on the side!