Bringing new meaning to the phrase “soup and sandwich,” this French onion grilled cheese recipe combines two classics—French onion soup and grilled cheese—into one decadent treat. And it’s a cinch to make. Bon appetit!
Heat 1 tablespoon butter and the olive oil in a large cast iron skillet over medium heat. When foam subsides, add onion; sauté until onion is translucent, about 5 minutes.
Reduce heat to medium-low; continue cooking until onion is golden brown, stirring occasionally, about 20 minutes longer.
Increase heat to high. Add broth to the skillet; cook until liquid has evaporated, about 3 minutes. Remove from heat. Stir in thyme; season with salt and pepper.
Spread one side of each bread slice with 1-1/2 tablespoons butter, dividing evenly. Place 2 bread slices, in a large cast iron skillet, buttered side down.
Top each with 2 cheese slices. Top with caramelized onions, dividing evenly.
Top each with 1 cheese slice. Cover with remaining bread, buttered side up.
Turn on heat to medium-low. Cook each sandwich until golden brown, 2 to 3 minutes per side.
Place 1 cheese slice on top of each sandwich. Place sandwiches under broiler just until cheese melts.
