In the bowl of a stand mixer fitted with the paddle attachment combine melted butter, flour, salt, and lukewarm water. Mix at medium speed about 1 minute until a smooth and elastic dough forms.
In a small saucepan (with a lid) bring water to a boil then remove the pot from the heat, empty the pot and dry it with a dish towel. Line the pot with a sheet of parchment paper, put the dough into the pot and put the lid on. Let sit for 30 minutes at room temperature.
Preheat the oven to 350°F (180°C) and line a baking sheet with parchment paper.
Meanwhile, in a small bowl combine raisins and rum. Let sit for 30 minutes. Then discard the rum.
Peel, core, and cut the apples into small stripes (batonnets, see image above). Combine apples with lemon juice. Add cinnamon, sugar, raisins, almonds, and vanilla extract. Set aside.
Lay a thin kitchen towel preferably with a pattern flat on the counter. Sprinkle with flour. Roll the dough out as thin as you can. Brush it with a little bit of melted butter.
Then use your hands to carefully stretch it until it is about 18x12 inches (45x30 cm) big and you're able to see the pattern of the dish towel through the dough.
Brush half of the melted butter over the rolled out dough.
The long side should be facing you. On the right side of the rectangle, leave a few inches space, then sprinkle the breadcrumbs top to bottom over the dough in a 6-inch thick line. Leave a 2-inch margin at the top and bottom of the strip.
Pile the apple filling on top of the breadcrumbs. Use a slotted spoon so the liquid stays in the bowl.
Fold the 2-inch margin at the top and bottom of the dough over onto the filling then roll up the strudel from the short side with the help of the towel. Tuck the ends.
Carefully transfer the Strudel to the prepared baking sheet, seam side down. Brush with a little bit of melted butter.
Bake for about 50 minutes in the lower third of the oven, until lightly golden on top. Brush strudel with remaining melted butter every 20 min while in the oven.
Let cool for 10 minutes then sprinkle with powdered sugar and serve warm.