Cook the spaghetti. Preheat the oven to 350°F. Bring a large pot of salted water to a full boil, then cook the thin spaghetti until al dente, approximately 8–10 minutes depending on the brand. Keep the noodles slightly firm because they will continue to cook during baking. Drain thoroughly and transfer the spaghetti to a large mixing bowl.

Coat the pasta. Whisk the eggs with the grated Parmesan in a small bowl until blended. Pour in the melted unsalted butter and stir until the mixture is uniform. Add this mixture to the drained spaghetti and toss carefully until the noodles are evenly coated.

Form the pasta and cream layers. Arrange the coated spaghetti evenly across the bottom of a 9 × 13-inch baking dish, gently pressing it into a level layer.

Combine the softened cream cheese, room-temperature sour cream, minced garlic, and Italian herb seasoning in a separate bowl. Stir until smooth and free of visible lumps. Spread the creamy mixture evenly over the spaghetti using the back of a spoon or an offset spatula.

Prepare and add the meat sauce. If the meat has not already been cooked, brown the Italian sausage or ground beef in a skillet over medium-high heat, breaking it into small crumbles as it cooks. Continue for approximately 8–10 minutes, then drain away the excess fat.

Stir the prepared spaghetti sauce into the cooked meat until thoroughly combined. Distribute the meat sauce evenly over the cream cheese layer, covering the surface completely.

Add the mozzarella and bake. Scatter the shredded mozzarella uniformly over the meat sauce. Transfer the dish to the preheated oven and bake for 45 minutes, or until the cheese is melted, bubbling, and beginning to develop a golden color. The sauce should also be visibly bubbling around the edges.

Remove the baked spaghetti from the oven and allow it to stand for 5 minutes before portioning. This brief resting period helps the layers hold together more neatly when served.