In a small bowl, mix together the mayonnaise, Dijon mustard, and pure maple syrup.
Lay out the ingredients for easy assembly.
Spread a generous layer of the mayonnaise mixture on one side of each slice of bread.
On the unspread side of one slice, layer the Brie cheese, turkey slices, apple slices, and baby arugula. Top with the second slice of bread, spread side up.
Spread the unsalted butter on the outside of each slice of bread.
Grill the panini in a press or skillet until golden brown and the cheese is melted.
Once grilled, remove from heat, let rest for a minute, then slice in half and enjoy!
