First things first. Preheat your oven to 375°F (190°C). This ensures your shells will bake evenly and thoroughly.

In a large pot, bring salted water to a boil. Cook those jumbo pasta shells according to package instructions, but stop about two minutes before they are fully al dente. You'll want them firm; they’ll finish cooking in the oven later.

Once done, drain the shells and set them aside. If you want to make things easier, toss them in a little olive oil to prevent sticking.

In a large skillet, heat one teaspoon of extra-virgin olive oil over medium heat. Add the finely chopped onion and garlic. Sauté until the onion is translucent, about 3-4 minutes. The aroma of these two together is simply irresistible.

Add the pound of lean ground beef to the skillet. Use a wooden spoon to break it up. Cook until browned, about 5-7 minutes. Drain any excess fat. Sprinkle in the dried oregano and, if you like a bit of heat, the crushed red pepper flakes. Stir to combine everything and let those spices mingle.

Next, add the thawed and thoroughly squeezed spinach to the beef mixture. Stir until it’s incorporated well. Remove the skillet from heat, allowing the filling to cool slightly.

In a large bowl, mix the ricotta cheese, one cup of the shredded Italian cheese blend, and half of the grated Parmesan cheese. Add the large egg and stir until combined. This mixture will make your shells unbelievably creamy.

Take a shell in one hand and a spoonful of the ground beef mixture in the other. Stuff the shell generously, making sure to pack it well. Place the stuffed shell seam-side up in a baking dish. Repeat this until all shells are filled.

Once the shells are nestled nicely in the dish, pour the marinara sauce over them. Make sure they’re evenly coated. Sprinkle the remaining shredded Italian cheese and Parmesan on top. This will create that magical cheesy crust we all love.

Cover the baking dish tightly with aluminum foil and place it in the preheated oven. Bake for about 25 minutes. Then, remove the foil and bake for another 10-15 minutes. This allows the cheese to become gloriously bubbly and golden.

Once the shells are ready, take them out of the oven and let them cool for a few minutes. Sprinkle some chopped fresh parsley on top for color. Dig in and let the flavors melt in your mouth!