Preheat your oven to 375°F (190°C) and grease a 9x13-inch baking dish.

Slice each mini croissant horizontally without cutting all the way through. Layer half a slice of cheese, a slice of ham, and another half slice of cheese inside each.

In a small bowl, mix softened butter, mustard, honey, and Worcestershire sauce until smooth.

Spread the butter mixture inside each croissant and pack them into the baking dish closely together.

Whisk the egg white until frothy and brush the tops of each croissant. Sprinkle poppy seeds if desired.

Bake for 15-18 minutes or until the cheese is melted and the tops are golden brown. Let cool slightly before serving.