# Directions:
01 - Combine flour, cornstarch, salt, pepper, and paprika in a shallow bowl. Pour buttermilk into a separate bowl for dipping.
02 - Dip onion slices into buttermilk, then dredge through flour mixture. Shake off excess coating and set aside.
03 - Heat 1 inch of vegetable oil in a skillet over medium-high heat. Fry onions in batches for 2-3 minutes until golden and crispy. Drain on paper towels.
04 - Butter one side of each bread slice. Place two slices butter-side down on a clean surface.
05 - Distribute half the cheddar and mozzarella over each slice. Add a layer of crispy fried onions, then remaining cheese. Top with remaining bread slices, butter-side up.
06 - Cook on a nonstick skillet or griddle over medium-low heat for 3-4 minutes per side. Press gently until bread turns golden brown and cheese melts completely.
07 - Let sandwiches rest briefly, then cut in half and serve while hot.