Begin by boiling a large pot of salted water and cook the lasagna sheets according to the package instructions until al dente, typically about 8-10 minutes. Once cooked, drain them in a colander and gently rinse with cold water to prevent sticking. Lay the sheets flat on a clean kitchen towel or parchment paper, keeping them separate for easy assembly of your Lasagna Roll Ups.

In a large skillet, heat a splash of olive oil over medium heat. Add the chopped onion and Italian sausage, cooking for about 5-7 minutes until the sausage is browned and the onions are tender. Stir in minced garlic, parsley, basil, oregano, and tomato sauce, bringing the mixture to a simmer. Let it cook for 10-15 minutes, allowing the flavors to meld beautifully, then remove from heat.

While the meat sauce simmers, preheat your oven to 350°F (175°C). This step is crucial as it ensures even baking for your Lasagna Roll Ups, making them deliciously bubbly and warm when serving. Prepare a baking dish by lightly greasing it, so the rolls do not stick during baking.

In a mixing bowl, combine the ricotta cheese, egg, 1/4 cup of grated Parmesan, 1 cup of shredded mozzarella, and fresh spinach. Mix everything together until well combined, forming a creamy and flavorful filling. This rich mixture will perfectly complement the hearty meat sauce in your Lasagna Roll Ups, bringing harmony to the dish.

Spread 1/4 cup of the meat sauce evenly across the bottom of your greased baking dish. Take each lasagna sheet, and spread 2 tablespoons of the ricotta mixture on it, followed by 2 tablespoons of meat sauce. Carefully roll up the sheet from one end to the other, placing it seam-side down in the baking dish. Repeat this step until all lasagna sheets are filled and rolled neatly.

Pour the remaining meat sauce over the assembled roll ups, ensuring they are well-covered. Sprinkle the remaining mozzarella and Parmesan cheese evenly on top, creating a lovely cheesy crust. Cover the baking dish with aluminum foil and bake in the preheated oven for 40 minutes, allowing the flavors to meld.

After 40 minutes, remove the foil from the baking dish and return it to the oven for an additional 5 minutes, or until the cheese is bubbly and golden. Once done, let the Lasagna Roll Ups cool slightly for about 5 minutes before serving. This resting time helps the flavors settle and makes them easier to cut and serve.