Cook the Lasagna Sheets: Bring a large pot of salted water to a rolling boil. Add the lasagna sheets and cook according to package directions until al dente—typically 8-10 minutes. You'll know they're ready when they are pliable and have a slight resistance to the bite. Drain in a colander and rinse with cold water to stop the cooking. Lay the sheets flat on a clean kitchen towel or baking sheet, making sure they don't overlap and stick together.

Prepare the Spinach Filling: While the pasta cooks, heat the olive oil in a large frying pan over medium heat. Add the chopped onion and cook, stirring occasionally, until it becomes translucent and fragrant, about 5 minutes. Add the minced garlic and cook for another minute until you can smell its aroma. Add the spinach in batches, stirring until it wilts completely—the pan will look very full at first, but the spinach will reduce significantly. Once all the spinach is wilted (you'll see the volume shrink by about half), remove the pan from the heat. Let it cool slightly, then transfer the mixture to a clean tea towel and squeeze out as much excess liquid as possible. This step is crucial for a firm, not watery, filling.

Make the Cheese Mixture: In a large bowl, combine the squeezed spinach mixture with the ricotta, beaten egg, grated Parmesan, half of the grated mozzarella, and the nutmeg. Season with salt and pepper. Stir everything together until you have a homogenous, creamy green filling. The texture should be thick and spreadable, not runny.

Assemble the Roll-Ups: Preheat your oven to 180°C (350°F). Spread a thin layer of marinara sauce (about ½ cup) over the bottom of a 9x13-inch baking dish. Take one cooked lasagna sheet and lay it flat on a clean surface. Spoon about 3 tablespoons of the ricotta-spinach mixture along the short edge of the sheet, leaving a 1-inch border at the sides. Gently but firmly roll the sheet away from you, tucking the filling inside as you go. Place the roll-up, seam-side down, into the prepared baking dish. Repeat with the remaining sheets and filling.

Top with Sauce and Cheese: Pour the remaining marinara sauce over the roll-ups, making sure to cover them completely. The sauce should be evenly distributed. Sprinkle the remaining mozzarella and a generous amount of extra grated Parmesan over the top. The cheese will create a golden, bubbly crust.

Bake to Perfection: Place the baking dish in the preheated oven and bake for 30-35 minutes. You'll know it's done when the sauce is bubbling vigorously around the edges and the cheese on top is melted and turning a deep golden brown. Let the dish rest for 5-10 minutes before serving. This resting period allows the rolls to set slightly, making them easier to lift out.

Garnish and Serve: Just before serving, scatter a few fresh basil leaves over the top for a pop of colour and freshness. Use a spatula to lift each roll-up out, ensuring you get some of the lovely sauce from the bottom of the dish. My husband, who's usually picky, asked for seconds the first time I made these!