In a small bowl, combine mayonnaise, honey, Dijon mustard, and maple syrup. Mix until smooth and set aside.

Lay out 4 slices of whole grain bread on a clean surface. Spread a generous layer of the honey mustard maple mayo on each slice.

On top of the mayo, layer the sliced turkey breast evenly across the 4 slices.

Add a layer of thin apple slices on top of the turkey, followed by slices of Brie cheese.

Top each sandwich with the remaining 4 slices of bread, mayo side down.

Heat a large skillet or panini press over medium heat. Spread softened butter on the outside of each sandwich.

If using a skillet, place the sandwiches in the pan and press down with a spatula. Cook for about 3-4 minutes on each side, or until the bread is golden brown and the cheese is melted. If using a panini press, cook according to the manufacturer's instructions.

Remove from heat, slice in half, and serve warm.