To make the dough:
Place the flour, egg, soft butter and salt in the bowl of an electric mixer. Mixing with the dough hook on low speed, add enough of the cold water to make a soft dough. Knead the dough in the electric mixer at medium speed until it is smooth and elastic, about 5 minutes. Form the dough into a ball and coat it with oil. Cover and let rest at room temperature for about 1 hour.
For the filling:
To make the coarse bread crumbs, toast slices of white bread in the oven until crisp, about 10 minutes. Break into pieces and place in a food processor. Pulse the processor until the bread resembles large bread crumbs. In a skillet over medium heat, cook the bread crumbs in 1/4 cup of the melted butter until they are golden brown. Reserve the sauteed bread crumbs and the remaining melted butter separately. Combine the sliced apples, granulated sugar, raisins, nuts, ground cinnamon and about half of the bread crumbs. Cut the firm butter into chunks and gently toss together with the apple mixture.
Cover a work surface with a clean piece of cloth. The cloth is used to facilitate stretching and rolling the dough. Make sure that the cloth is securely fastened to the table. Dust the cloth lightly with the flour. Place the rested dough in the center of the cloth. Using a rolling pin, roll the dough into a large, thin rectangle. When the dough is as thin as it will go with the rolling pin, it is time to begin stretching and pulling the dough. To stretch and pull the dough, place your hands under the dough, and, using your thumbs and the back of your hand, gently begin pulling and stretching the dough. Pull and stretch the dough until it is a rectangle approximately 3 1/2 feet by 2 1/2 feet. Be very careful when you are pulling and stretching not to tear the dough. After it is pulled to the proper size, let the dough to relax on the table for a few minutes. There will be a thick edge around the edges, trim this away. You also want to trim off any parts of the dough that hang over the edges of the table. Place the apple filling next to the long edge of the dough closest to you. Form the filling into a thick log. Brush some of the reserved melted butter generously over the remainder of the dough. Sprinkle the remaining bread crumbs over the dough.
Using the cloth to help lift the dough, roll the strudel as you would a jelly roll, starting from the filling side. Place the strudel, seam side down, in a horseshoe shape on a sheet pan lined with parchment paper. Brush the strudel with the last of the melted butter. Bake in a preheated 375ºF oven for about 35 minutes, Remove the pan from the oven and cool. Slice the strudel into individual servings and serve either warm or at room temperature.
Yield: about 16 servings