The day before baking the strudel, place raisins and rum in a small bowl. Cover and let sit overnight.
To make the filling, peel, slice and core the apples. Cut each slice in half and place in a large bowl. Add the lemon juice, sugar and cinnamon. Pour over the raisins and rum. Gently stir to combine. Set aside.
In a small saucepan over medium heat, melt 2 Tablespoons of butter. Add the breadcrumbs, vanilla and a pinch of salt. Stir to coat the bread crumbs and cook until fragrant and golden brown, about 5 to 8 minutes. Stir frequently to make sure the breadcrumbs don’t burn. Remove from the heat and transfer to a plate.
Melt the remaining 2 Tablespoons of butter and set aside.
Preheat the oven to 400°F. Line a large rimmed baking sheet with parchment paper.
Place one roll of phyllo dough on a lightly floured work surface. Use a rolling pin to roll lightly into an approximate 10-inch by 12-inch rectangle. Carefully place on the parchment-lined baking sheet. Brush with some of the melted butter.
Sprinkle half the breadcrumbs down the middle of the pastry dough. Discard any juices from the filling and arrange half of the apple filling down the center as well. There should be about 3 inches of exposed dough on both sides of the filling.
Use a sharp knife to cut the exposed dough into 2-inch thick strips. Criss-cross the dough strips over the apple filling, tucking the ends under.
Whisk together the egg and water and brush over the pastry dough. Repeat the process with the second dough and remaining breadcrumbs and apple mixture.
Bake at 400℉ for 30 to 40 minutes. Halfway through the baking time, rotate the baking sheets. Cool for 15 minutes before dusting with confectioners’ sugar and serving. This can also be served with vanilla ice cream alongside.
Notes
Apples: Crisp apples, such as Granny Smith or Honeycrisp, are best for baking since they maintain their texture.Rum: If you don't have rum on hand, you can use bourbon or brandy. For a nonalcoholic version, use apple cider or apple juice.Phyllo dough: This provides the most authentic version of strudel dough without making it from scratch. If you like a more buttery texture, use puff pastry.Store leftovers in an airtight container in the refrigerator for up to 4 days. Strudel is best when eaten the day it is baked.