After Christmas dinner, there's still room for dessert. Apple strudel is light enough for everyone to take a bite. You can prepare the strudel ahead of time.
Have ready a 24-by-24-inch sheet of clear plastic or two pieces of parchment. Generously butter a large baking pan. Sprinkle with flour, and tap out the excess; set aside. Place flour, 8 tablespoons butter, 3 eggs, salt, 1 teaspoon sugar, and 1 tablespoon water in the bowl of a food processor, and pulse until dough comes together. Divide dough in half equally, flatten into two disks, and wrap each in plastic wrap. Refrigerate 2 to 3 hours or overnight.
Preheat the oven to 375 degrees. Place bread in the clean bowl of a food processor; pulse until crumbly; set aside. Melt 10 tablespoons butter in a large skillet set over medium-low heat. Add pine nuts and breadcrumbs, and cook, stirring frequently, until fragrant and golden brown, 8 to 10 minutes; set aside.
Melt 2 tablespoons butter in a large Dutch oven over medium-high heat. Add sliced apples and remaining sugar; cook, stirring frequently, until apples have softened, 10 to 12 minutes. Remove from heat; transfer apples to a large bowl. Stir in the pine-nut mixture, lemon zest, and raisins, and set aside to cool, about 15 minutes.
Place egg yolk in a small bowl, and stir to break it open; set aside. In a small skillet on low heat, melt the remaining 2 tablespoons butter; set aside. Spread the plastic sheet on a clean surface, and dust with flour. Remove dough from refrigerator, and place it in the center of the plastic sheet or on parchment. Roll out into a 20-inch diameter paper-thin circle. Brush the dough with melted butter. Spread half of the reserved apple mixture on the dough. Lift the front edge of the plastic up, and fold the dough over the apple mixture and away onto itself. Repeat folding procedure, ending with the raw edge on top. Gently lift edge, and brush with egg yolk and gently press to seal. Brush ends of dough with egg; fold up; seal. Repeat process with second piece of dough. Transfer to prepared baking pan. Brush surfaces with egg yolk. Using a wooden skewer, pierce the strudels all over.
Transfer to oven; bake, rotating pan once halfway through, until golden brown, 30 to 35 minutes. Remove from oven; transfer pan to wire rack to cool, about 45 minutes. Sprinkle with confectioners' sugar; serve.