01 - Preheat the oven to 400°F. Lightly grease a 2-quart baking dish with butter or cooking spray.
02 - Bring a large pot of salted water to a boil. Add pasta and cook until al dente according to package directions. Drain well and set aside.
03 - In a large skillet over medium heat, melt the butter. Add chopped onion and cook until softened and translucent, about 4 minutes. Add minced garlic and sauté for 1 minute until fragrant.
04 - Add chopped spinach to the skillet and cook until wilted, about 2-3 minutes. Season with salt, pepper, Italian herbs, and nutmeg.
05 - Reduce heat to low. Add cream cheese and stir until melted and incorporated. Gradually pour in the whole milk and heavy cream, stirring constantly until smooth and combined.
06 - Add half of the shredded mozzarella and half of the grated Parmesan. Stir until completely melted and the sauce reaches a creamy consistency.
07 - Add the cooked pasta to the creamy sauce mixture. Stir gently until all pasta is evenly coated.
08 - Transfer the pasta mixture to the prepared baking dish, spreading it evenly.
09 - Sprinkle the remaining mozzarella and Parmesan cheese evenly over the pasta.
10 - In a small bowl, combine panko breadcrumbs with olive oil. Toss until breadcrumbs are lightly coated.
11 - Sprinkle the oiled breadcrumbs evenly over the cheese layer.
12 - Bake for 20 minutes or until cheese is melted and bubbly, and the breadcrumb topping is golden brown.
13 - Remove from oven and let rest for 5 minutes before serving to allow the dish to set.