01 -
Preheat the oven to 190°C. Lightly butter a medium-sized baking dish.
02 -
Place onion slices in a single flat layer in the prepared dish.
03 -
Season onions evenly with salt, freshly ground black pepper, and Italian seasoning. Distribute butter pats over the seasoned onions.
04 -
Scatter shredded mozzarella over onions, then place provolone slices across the top. Finish with an even layer of grated Parmesan.
05 -
Bake uncovered for 25 to 30 minutes until the cheese is golden and bubbling.
06 -
For extra crispness, broil for an additional 2 minutes watching closely to avoid burning.
07 -
Allow dish to rest for 5 minutes before serving to let flavors meld and cheese set.