For the strudel dough:
In a medium bowl or the bowl of a stand mixer, combine flour, salt, vinegar, oil, and water.
Mix into a soft but slightly sticky dough. Knead for 10 mins.
Turn the dough ball onto a work surface. With your hands, knead the dough in a stretch-and-fold method. Form the dough into a smooth ball.
Rub the entire dough ball with a little bit of oil, place it in a small bowl, and cover tightly with plastic wrap.
Let the dough rest in a warm spot for at least one hour.
For the filling:
In a small skillet, melt 4 TBSP of butter. Add the bread crumbs and toast them over low-medium heat until fragrant and lightly browned. Transfer the breadcrumbs to a small bowl and set aside.
Peel, core, and quarter the apples. Cut them into very thin slices and place them in a medium bowl.
Combine the apples with raisins, chopped nuts, bread crumbs, and lemon juice (if the apples are on the sweet side). Mix well.
Combine the sugar with the ground cinnamon and set aside.
Preaheat the oven to 400˚F.
Once the dough has rested for at least one hour, place the dough ball onto a lightly floured surface. With a floured rolling pin, roll into a rectangle.
Lightly flour a heavy kitchen towel. Place the dough onto the kitchen towel. Using a rolling pin or your hands, roll and stretch the dough until it is so thin that you can see the towel shine through.
Add the cinnamon-sugar to the apples and mix well.
Place the apples to about ⅓ of the stretched dough and press the apple mixture down.
Fold the sides of the dough in. Using the towel, roll the dough from the apple side like a jelly roll, pressing the apple mixture as you go.
Carefully transfer the strudel roll onto a baking sheet lined with parchment paper. Brush melted butter over the top of the strudel.
Bake the strudel in a preheated oven for 30 mins or until golden-brown.
Remove the apple strudel from the oven, brush with more melted butter, and let cool down.
Make the vanilla sauce:
Over low-medium heat, in a heavy saucepan, heat 1 ¾ c of milk.
Combine the remaining ¼ c of milk with the vanilla, sugar, starch, and egg yolks.
Before the milk reaches boiling, remove from heat. While constantly stirring, whisk in the milk slurry. Return the saucepan to the low heat. Continue to stir until the sauce thickens.
Generously sprinkle the apple strudel with powdered sugar.
Serve a slice of warm apple strudel with a a big helping of vanilla sauce.