COMBINE mustard, shallot, honey and thyme in a small bowl. Season with salt and pepper to taste. Cover and refrigerate until ready to use.
PREHEAT oven to 375°F.
LATHER cut side of croissants with thyme honey mustard mixture.
LAYER ham, cheese and apple slices on bottom half of croissant.
TOP sandwich with top half of croissant.
BRUSH croissants with beaten egg white and sprinkle with poppy seeds.
BAKE 10 minutes, until cheese is melted and tops of croissants are deep golden-brown.