Heat olive oil in a large, oven-safe skillet over medium heat. Add the chopped onion and cook until softened, about 3 minutes. Stir in the minced garlic, Italian seasoning, and red pepper flakes (if using), cooking for another minute until fragrant.

Step 2: Build the Sauce

Add the chopped sun-dried tomatoes and baby spinach to the skillet. Stir until the spinach wilts slightly. Pour in the heavy cream, whole milk, and broth, stirring to combine. Let the mixture simmer for 2-3 minutes to develop flavor.

Step 3: Add the Ravioli and Cheese

Gently fold in the fresh ravioli, ensuring they are evenly coated in the sauce. Sprinkle in the Parmesan cheese, stirring gently until melted. Season with salt and black pepper.

Step 4: Top and Bake

Sprinkle the shredded mozzarella cheese evenly over the top. Transfer the skillet to a preheated 375°F oven and bake for 20-25 minutes, until the cheese is golden and bubbling.

Step 5: Garnish and Serve

Remove from the oven and let rest for 5 minutes. Sprinkle with fresh basil before serving.