Preheat your oven to 350°F and prepare 2 baking sheets lined with parchment paper.

Take the filo dough out of the fridge and let it sit on the counter for about 15-20 minutes.

In a large mixing bowl, combine the thinly sliced apples, brown sugar, granulated sugar, cinnamon, and sea salt. Mix well and set aside.

Remove the filo dough from the package and cover it with damp paper towels to prevent it from drying out.

Brush a light coating of melted butter on the parchment paper. Place 1 sheet of filo dough on top of the parchment. Lightly brush this sheet with butter, then add another sheet on top. Repeat this process until you have 8 sheets of filo dough stacked and buttered.

Place half of the apple mixture (leaving behind any juices) down the center of the stacked filo dough, leaving 2-3 inches of space along the edges.

Gently fold the ends over, brush with butter, then fold one side over, brush with butter, and carefully roll the strudel over onto its seam. Lightly brush the top with butter and sprinkle with a bit of granulated sugar and cinnamon if desired. Repeat the process with the remaining apples and filo dough.

Bake for about 28 minutes, until the strudel is golden. Let it cool slightly before serving.