Mix the mayonnaise and Dijon mustard together in a small bowl. Set aside in the refrigerator until ready to use.
Season the burger patties generously with salt and pepper on both sides.
Grill over medium-high heat for about 4 to 5 minutes per side depending on thickness and your preferred doneness.
In the last 7 minutes of cooking, lay the Brie slices over each patty and close the grill lid. Let the cheese melt completely over the burger.
Toast the brioche buns cut side down on the grill for about 1 minute until golden.
Build the burgers. Spread apple butter on the bottom bun. Add the Brie-topped burger patty. Layer on the crispy bacon, thin apple slices, and arugula. Drizzle hot honey over the top. Spread the Dijon mayo on the top bun and close the sandwich.
Serve immediately.