Follow these step-by-step instructions to prepare your shrimp and spinach stuffed shells:

1. Preheat and Prepare

1. Preheat your oven to 375°F (190°C).
2. In a large pot of salted boiling water, cook the jumbo pasta shells until al dente, following the package instructions. Drain and set aside.

2. Prepare the Filling

1. In a large skillet, heat 1 tablespoon of olive oil over medium heat.
2. Add the minced garlic and sauté for about 1 minute until fragrant.
3. Add the chopped shrimp to the skillet and cook until pink and opaque, about 3-4 minutes. Remove from heat.
4. In a large mixing bowl, combine the cooked shrimp, chopped spinach, ricotta cheese, half of the mozzarella cheese, half of the Parmesan cheese, and the egg. Mix well.
5. Season with Italian seasoning, salt, and pepper. Stir until all ingredients are well incorporated.

3. Stuff the Shells

1. Spread 1 cup of marinara sauce on the bottom of a 9×13 inch baking dish.
2. Carefully fill each cooked pasta shell with the shrimp and spinach mixture and place them seam side up in the prepared baking dish.

4. Prepare the Sauce

1. In a separate bowl, combine the remaining marinara sauce with the heavy cream. Mix until smooth.
2. Pour the creamy marinara sauce over the stuffed shells in the baking dish.

5. Bake

1. Sprinkle the remaining mozzarella and Parmesan cheese over the top of the shells.
2. Cover the baking dish with foil and bake in the preheated oven for 25 minutes.
3. Remove the foil and bake for an additional 10 minutes, or until the cheese is bubbly and golden brown.

6. Serve

1. Remove the dish from the oven and let it cool slightly.
2. Garnish with fresh basil, if desired, and serve hot.