Double Crunch Ham & Cheese Sandwich

1 . Stage

Build the sandwiches: Arrange slices of bread in a single layer on a work surface. Brush the top sides of each piece of bread with the butter. Flip the bread so the butter side is down. Spread mustard on top of half of the slices of bread. Sprinkle each piece (the ones spread with mustard and the ones without mustard) of the bread with the gruyere and cheddar cheeses. 

2 . Stage

Set aside the mustard and cheese slices for closing the sandwiches. For the remaining slices with just cheese, top with an even layer of pretzels, then with a layer of the ham, followed by an even layer of the apple. Close the sandwiches with the reserved pieces of bread, butter side facing out. 

3 . Stage

Heat a large skillet over medium-low heat. Place 2 sandwiches in the skillet and cook until the bottom slice of bread is golden and the cheese is starting to melt, about 5 minutes. Carefully flip the sandwich and cook until golden underneath, about 5 minutes more. Repeat with remaining sandwiches. Slice and serve hot.