Using a 2-inch round cutter, cut 12 circles from frozen bread. To prevent bread rounds from drying out, place frozen bread in a resealable plastic bag to let thaw at room temperature.
Using a sharp paring knife, cut thin slices vertically from apple. Using a 2-inch round cutter, cut 6 circles from apple slices, including an edge of peel. Using same cutter, cut 6 circles from cheese slices.
Spread a thin layer of Dijon Mayonnaise onto bread rounds. Place small lettuce leaves on top of mayonnaise side of 6 bread rounds, trimming excess lettuce. Top each with a ruffled piece of ham, an apple round, and a cheese round. Cover with remaining bread rounds, mayonnaise side down. Secure with a decorative pick, if desired. Serve immediately, or cover with damp paper towels, place in a covered container, and refrigerate until serving time.
Recipe by TeaTime Magazine at https://teatimemagazine.com/ham-green-apple-tea-sandwiches-recipe/