Heat the oven to 400°F. Line a baking sheet with a piece of parchment paper.
Melt the remaining 5 tablespoons (75 grams) of butter in a small pan and set aside.
On your work surface, spread out a clean cotton or linen kitchen towel that measures at least 24 by 32-inches (I use a folded bed sheet). The long side of the towel should be horizontal and the short side vertical; this is how you want the dough to be positioned later when you fill it.
Sprinkle flour lightly over the towel. Place the dough in the middle of the towel and roll it out several times in both directions with a rolling pin until it’s about 10 by 13 inches. Then ball your hands to loose fists, put them under the rolled-out dough, and gently start stretching out the dough using the back of your hands. Alternate with pulling on the dough gently with your fingers to continue stretching the dough. This takes patience and some confidence. You don’t want the dough to rip, but you do need to stretch out the dough with some assertiveness. If it does rip, press the dough together again around the rip.
Continue stretching out the dough evenly until it measures 16 by 24 inches and is thin enough that you can see the pattern of the towel through it. Make sure you pull the edges of the dough as thin as you can, too. The dough should be uniformly thin all over.
Brush the dough evenly all over with some of the melted butter. On the right side of the rectangle, distribute the toasted, lightly sweetened bread crumbs from top to bottom over one-quarter of the dough, leaving 1 ¼-inch border at the edges on the top, bottom, and right.
Drain off any juices that have accumulated at the bottom of the bowl of apples and raisins, and then pile the apple mixture evenly over the bread crumbs. Gently pull the top and bottom edges of the dough over the sides of the filling, stretching slightly if necessary, and then pull the right edge of the dough up and over the filling as far as it will go without tearing. Working carefully, use the towel to roll up the strudel all the way.
Using the towel as a sling, gently roll the strudel onto the baking sheet with the bread crumbs and the seam on the bottom. If the strudel roll feels sturdy enough, you can instead transfer the roll with your hands. If the strudel is lumpy or larger at one end than the other, use your hands gently but firmly to form the strudel into a uniform shape–it should be the same thickness all the way along its length. Brush the strudel liberally and thoroughly with more of the melted butter.
Place the baking sheet in the oven and bake the strudel for 15 minutes; remove from the oven and brush the strudel thoroughly all over with more of the melted butter. Rotate and bake for another 15 minutes; remove again and brush liberally with the remaining butter. Rotate again and bake for an additional 10 to 15 minutes. When ready, the strudel should be crisp to the touch and a deep golden brown.
Remove the baking sheet from the oven and put it on a rack to cool for at least 20 minutes before serving. Dust with confectioners’ sugar and slice into 2-inch pieces to serve, with schlagsahne (whipped cream) or vanilla ice cream alongside. Strudel is best the day it is made, but it keeps 1 to 2 days at room temperature. Before serving, crisp up leftover strudel in a 350°F oven for a few minutes.