To make the honey mustard, simply combine all the ingredients in a small bowl and stir.
Spread the outsides of the bread with softened butter and spread the inside surfaces with the honey mustard. Assemble sandwiches by layering the ham, apple, and Brie on 4 slices of bread, then top with the remaining slices of bread. Using a griddle or a Panini press, grill the sandwiches until they are golden brown and crisp on the outside.
Whisk the shallot, honey, vinegar, and oil. Season to taste with salt and pepper, then toss with spring greens or arugula.