In a medium saucepan, melt the butter over medium heat. Add the diced apples, brown sugar, cinnamon, cardamom, ginger, and salt.

Cook, stirring occasionally, until the apples are softened but not mushy, about 8-10 minutes. They should release some of their juices, creating a slightly syrupy sauce.

Remove the saucepan from the heat and let the apple mixture cool completely. This is important because a hot filling will melt the puff pastry.

Gently unfold the thawed puff pastry sheet on a lightly floured surface.

Roll it out slightly with a rolling pin to smooth out any creases and make it a bit thinner.

Use a sharp knife or a pizza cutter to cut the puff pastry into 6 large triangles.

Place a spoonful of the cooled apple filling at the wide end of each triangle.

Starting from the wide end, gently roll up each triangle towards the point.

Curve the ends slightly to create a crescent shape.

Place the rolled croissants on a baking sheet lined with parchment paper.

In a small bowl, whisk the egg with a tablespoon of water. Brush the tops of the croissants with the egg wash.

Sprinkle the tops with coarse sugar, if desired.

Bake in a preheated oven at 375°F (190°C) for 20-25 minutes, or until the croissants are golden brown and puffed up.

Let the croissants cool on the baking sheet for a few minutes before serving.