In a large mixing bowl, whisk together the all-purpose flour, potato flour, sugar, instant yeast, and salt.

In a separate bowl, combine the soft butter, egg, vanilla extract, and lukewarm milk. Gradually pour the wet ingredients into the dry mix, stirring until a shaggy dough forms.

Let this mixture rest for 30 minutes, allowing the yeast to activate and the flavors to meld.

After resting, turn the dough onto a lightly floured surface and knead for about 5-10 minutes until smooth and elastic.

Place the kneaded dough into a greased bowl, cover with a towel, and let it rise in a warm area for 1.5 to 2 hours.

While the dough is rising, prepare the filling by cooking the peeled grated apple in a saucepan over medium heat with lemon juice, sugar, cornstarch, salt, and cinnamon.

Cook for about 5-7 minutes until thickened and apples soften. Remove from heat and cool completely.

Once the dough has risen, punch it down gently and roll out into a rectangle about ¼ inch thick. Spread half of the apple filling evenly across.

Carefully roll the dough into a log, slice in half lengthwise, and twist the two sections together.

Repeat with remaining dough and filling. Place on a parchment-lined baking sheet and let rise for another 1 to 2 hours.

Preheat your oven to 350°F (175°C). Bake for 30-40 minutes or until golden brown and hollow when tapped.

Let cool on a wire rack for 1 hour. Prepare the glaze by mixing powdered sugar, vanilla extract, and a splash of water or apple juice.

Drizzle over the cooled bread for a sweet finish.