Preheat your oven to 190°C (375°F). Cook the jumbo pasta shells according to package directions until al dente, being careful not to overcook them. They should still have a slight bite. Drain the shells and rinse them with cool water to stop the cooking process. Set aside.

While the pasta is cooking, prepare the filling. Heat 30ml (2 tbsp) of olive oil in a large skillet over medium heat. Add the minced garlic and sauté for about 1 minute until fragrant, being careful not to burn it. Add the thawed and squeezed-dry spinach to the skillet. Cook for 3-5 minutes, stirring occasionally, until any remaining moisture has evaporated. Remove from heat and let it cool slightly.

In a large bowl, combine the ricotta cheese, grated Parmesan cheese, the beaten egg, nutmeg, 5g (1 tsp) salt, and 2.5ml (1/2 tsp) black pepper. Add the cooled spinach mixture to the bowl. Stir everything together until well combined. Taste and adjust seasoning if necessary.

Spread about half of the marinara sauce (approximately 350g or 12.3 oz) evenly over the bottom of a 23x33 cm (9x13 inch) baking dish. This will prevent the shells from sticking and add extra flavor.

Carefully stuff each cooked jumbo pasta shell with the spinach ricotta filling. You can use a spoon or a small piping bag for this. Arrange the stuffed shells in a single layer over the marinara sauce in the baking dish.

Pour the remaining marinara sauce (approximately 350g or 12.3 oz) over the stuffed shells, ensuring they are mostly covered. Sprinkle the shredded mozzarella cheese evenly over the top.

Cover the baking dish tightly with aluminum foil. Bake in the preheated oven for 20 minutes. Remove the foil and continue baking for another 10-15 minutes, or until the sauce is bubbly and the cheese is melted and lightly golden brown. Let the stuffed shells rest for 5-10 minutes before serving.