In a large mixing bowl, combine all-purpose flour, salt, sugar, and baking powder. Cut in cold unsalted butter using a pastry cutter until the mixture resembles coarse crumbs. Beat an egg and add it to the mixture, stirring until it just comes together. Wrap the dough in plastic wrap and refrigerate for at least 1 hour, preferably overnight.

After chilling, lightly flour your work surface and roll out the dough into a large rectangle, approximately 10x14 inches. Spread the apple pie filling down the center, leaving space on the edges. Fold the sides over to create an oval shape, ensuring to pinch the edges tightly to seal.

Preheat your oven to 375°F (190°C). Brush the top of the kringle with an egg wash made from a beaten egg and a splash of water. Bake in the preheated oven for about 25-30 minutes, or until golden brown and flaky.

Allow the kringle to cool for about 10 minutes. Prepare the glaze by whisking together sifted powdered sugar, vanilla extract, and a few tablespoons of water until smooth. Drizzle over the warm kringle.