In a small bowl, whisk the honey mustard dressing ingredients together. Spread a small amount of dressing onto all 4 slices of bread.
Arrange chicken evenly onto 2 of the slices of bread, and season with fresh cracked pepper, followed by arugula, then sliced apples, and finally the brie cheese slices. Top with the other slices of bread.
Preheat a flat-top griddle or skillet on med-high heat. Butter the top slice of bread, and place the sandwich buttered side down on the flat-top. While the first side is cooking, butter the second side of the bread. Cook for about 5-7 minutes or until golden brown. Flip and cook the second side until golden brown and cheese is melted.
Slice in half and serve along side the honey mustard dipping sauce.
I like to trim the rind off of the brie cheese. It has a distinct flavor that I am not a fan of, but you can certainly leave it on.
I highly recommend using sourdough bread, it just grills up so nicely for these! I get mine pre-sliced in the bakery section of my local grocery store.