First, follow the directions for the gluten-free puff pastry dough. If using Schar brand, thaw the dough at room temperature for at least 4 hours.
Then, peel and dice the apples and set them aside. (I use a sweeter variety of apples since this recipe is lower in added sugar)
Melt the butter in a medium size saucepan over the stove on medium-low heat.
Next, add to the saucepan the diced apples, coconut sugar, cinnamon, cardamom, salt, and corn starch. Stir all ingredients together and allow it to simmer on the stove for a total of 5 minutes while frequently stirring. Then remove it from the heat.
Preheat the oven to 400°F and place parchment paper over a cookie sheet. (Only use a pan that can withstand that temperature)
Remove a roll of dough from the box and gently roll it out on a flat surface. Use a knife or a pizza cutter and cut the dough into 4 equal squares. Use your hands to mend any cracks in the dough.
Then scoop out about 1 ½ tablespoons of apple filling, spreading it in the center of each square. Make sure to leave space around all edges of the dough. Fold the dough in half and pinch the dough together to seal all of the edges. Repeat the steps with the second roll of dough, but only fill the dough when it is ready to bake so it does not become soggy.
Next, take a knife and make 2 slits in the top of each strudel, enabling the steam to escape while baking.
Place the strudels on the baking sheet and bake them on the middle oven rack for 25 minutes or until golden-brown. Allow them to cool for 5 minutes before transferring them with a spatula to a cooling rack.
Finally, serve as is or serve them dusted with a little powdered sugar.