Bring a large pot of generously salted water to a rolling boil. Add the protein pasta and cook until al dente. Reserve 1 cup of the pasta water before draining the pasta and set it aside.

Heat 1 tablespoon of olive oil in a large, deep skillet over medium-high heat. Add the lean ground beef and break it apart with a wooden spoon. Season with salt and pepper. Cook undisturbed for a few minutes to develop a deep, caramelized crust. Transfer the beef to a plate, leaving a couple of tablespoons of drippings in the pan.

Reduce the heat to medium. Add a small pat of butter to the pan along with the diced onion. Cook for 3 to 4 minutes, stirring occasionally, until the onion turns translucent and soft. Add the minced garlic and cook for just 30 seconds until fragrant.

Lower the heat to medium-low. Add the cream cheese to the pan. Let it soften for a minute, then stir it into the onion mixture until it has completely melted and formed a smooth base. Slowly pour in the heavy cream, whisking constantly. Bring the sauce to a gentle simmer. Stir in the Italian seasoning and a pinch of red pepper flakes if using them.

Return the browned beef to the skillet along with any juices that accumulated on the plate. Stir to coat the beef in the sauce. Add the cooked pasta and toss everything together. Add handfuls of fresh spinach and stir until the spinach has just wilted into the creamy sauce.

Remove the pan from the heat. Stir in a generous handful of freshly grated Parmesan cheese. If the sauce is too thick, add a splash of the reserved pasta water to loosen it up. Taste and adjust the seasoning with more salt or pepper. Serve immediately while it is hot and luscious.