Preheat the Oven: Begin by heating your oven to 350°F (175°C). Preheating is essential for even cooking.
Prepare the Dish: Spray a 9×13-inch baking dish with non-stick cooking spray to prevent sticking while baking, ensuring that your dish comes out perfectly.
Slice the Onions: Clean and peel the Vidalia onions. Carefully slice them into ¼-inch rounds, ensuring that you do not separate them into rings. This helps maintain a nice texture during baking.
Arrange & Season: Spread the sliced onion rounds evenly across the baking dish. Season the layers generously with salt, garlic powder, and oregano. This step is crucial to enhance the flavors of the onions.
Add Butter & Cheese: Dot the top of the onions with unsalted butter, distributing it evenly. Next, layer the shredded Italian blend cheese and cheddar cheese generously over the onions. Finish with a topping of freshly shredded Parmesan cheese for an extra cheesy experience.
Bake: Place your dish in the preheated oven, baking for 35-40 minutes. You will know it’s done when the cheese is bubbly and golden, and the aroma fills your kitchen.
Serve: For the best experience, enjoy your Tennessee Onions while warm. The combination of textures and flavors will be at its peak, ensuring a satisfying dish.