Caramelized Red Onion and Apple Grilled Cheese Sandwich

Yield: 12 sandwiches

Caramelized Red Onions:
¼ cup butter
8 red onions, sliced (approximately 4 lb.)
2 tsp. salt

Grilled Cheese:
1 ½ cups butter, softened
24 slices crusty bread, about 1” thick
¾ cup grainy mustard
6 tart, crisp apples such as Granny Smith, Cortland or Fuji, cored and thinly sliced
12 slices applewood-smoked Cheddar cheese

For caramelized red onions: Melt butter in a large heavy-bottomed pan over medium-low heat. Cook onions, stirring often, for 60 to 90 minutes or until golden brown. Season with salt and cool completely.

For each sandwich: Between slices of bread, spread 1 Tbsp. mustard, 3 oz. apple slices (about ½ apple), 1 slice cheese and ¼ cup caramelized onions. Butter outer bread slices. Cook sandwich over medium-low heat until golden brown on each side and cheese is melted. Cut in half before serving.