Step 1: Prepare the Pasta

1. Preheat the oven to 375°F (190°C).
2. Bring a large pot of salted water to a boil. Add penne pasta and cook according to package instructions until al dente (about 9-10 minutes).
3. Drain the pasta and set it aside.

Step 2: Make the Alfredo Sauce

1. In a large skillet over medium heat, melt the butter. Add the minced garlic and sauté for 1-2 minutes until fragrant but not browned.
2. Pour in the heavy cream and milk, stirring well to combine. Bring the mixture to a gentle simmer, stirring frequently.
3. Gradually add 1 cup of grated Parmesan cheese, stirring continuously until the cheese melts and the sauce becomes thick and creamy (about 4-5 minutes).
4. Season the sauce with salt, black pepper, Italian seasoning, and red pepper flakes (if using). Stir well to incorporate all seasonings.

Step 3: Combine Pasta and Sauce

1. Add the cooked penne to the skillet with the Alfredo sauce, stirring until each piece of pasta is thoroughly coated.
2. Sprinkle in half of the shredded mozzarella cheese and stir to combine. The cheese will melt slightly into the sauce, making it extra creamy.

Step 4: Assemble the Casserole

1. Grease a 9×13-inch baking dish with olive oil.
2. Pour the Alfredo-coated pasta into the prepared baking dish, spreading it out evenly.
3. Sprinkle the remaining mozzarella cheese and ½ cup Parmesan cheese evenly over the top.

Step 5: Bake the Alfredo Penne

1. Place the baking dish in the preheated oven and bake for 20-25 minutes, or until the cheese on top is melted, bubbly, and slightly golden-brown.
2. For a more browned crust, switch the oven to broil for the last 2-3 minutes of baking. Keep a close eye to prevent burning.

Step 6: Garnish and Serve

1. Remove the baked pasta from the oven and let it sit for 5 minutes to set.
2. Sprinkle fresh basil over the top before serving.