Step 1: Preheat the Oven

Preheat your oven to 375°F (190°C). Lightly grease a 9×13-inch baking dish with non-stick spray or butter.

Step 2: Slice the Onions

Peel the onions and slice them into ¼-inch thick rounds. Separate the rings gently with your fingers. This helps with even layering and flavor absorption.

Step 3: Layer the Onions

Arrange the sliced onions in the baking dish in an even layer. You can slightly overlap them for a denser, more flavorful dish.

Step 4: Add Butter and Seasoning

Dot the butter pieces evenly over the onions. Sprinkle garlic powder, onion powder, salt, and pepper across the top. This seasoning combo deepens the dish’s savory appeal.

Step 5: Add Cheese

Sprinkle the mozzarella and cheddar cheeses evenly over the onions. Top with Parmesan cheese for an extra salty, umami-rich finish.

Step 6: Bake

Cover loosely with foil and bake for 25 minutes. Remove the foil and continue baking for another 20-25 minutes, or until the cheese is bubbly and lightly golden brown.

Step 7: Garnish and Serve

If desired, sprinkle chopped fresh herbs like thyme or parsley over the top before serving. Serve hot and enjoy!