Instructions

1. For the filling: Put raisins and wine into a small bowl and set aside to macerate for 30 minutes. Melt butter in a medium skillet over medium heat. Add walnuts and bread crumbs and cook, stirring often, until bread crumbs are golden, 3–5 minutes. Add raisins and wine, lemon juice, sugar, and salt and cook, stirring often, until filling sticks together when pressed with back of spoon, about 1 minute. Set aside to cool.
2. For the dough: Put milk, oil, and vanilla into a small bowl and set aside. Sift flour, sugar, and baking powder together into a large bowl. Stir in egg yolk; add milk mixture and stir until dough comes together. Turn dough out onto a clean surface and knead until smooth, 8–10 minutes. Divide dough in half and shape each piece into a rectangle. Lay out 2 large sheets of parchment paper on a clean surface and put dough rectangle in center of each with long sides of dough running parallel to long edges of parchment. Roll out dough to 9" × 11" rectangles.
3. Bring a large wide pot of water to a boil over high heat, then reduce heat to medium-low to maintain a gentle simmer. Meanwhile, position 1 piece of parchment with a long edge horizontal to edge of work surface. Spread half the filling down center of dough, leaving a 1" border on each end. Grab edge of parchment closest to you with both hands and lift up and over filling, folding dough onto filling only, then peel parchment away from dough. Turn parchment around so that opposite side is closest to you. Brush edge of dough closest to you with egg white, then fold edge over so that dough edges overlap slightly. Brush 1 of the short ends of dough with egg white and fold edge over by 1" to seal end. Gently press out any air pockets along length of stuffed dough, then brush other short end of dough with egg white and fold edge over by 1" to seal end. Transfer stuffed dough to center of a large piece of double-layer cheesecloth, peel off parchment, snugly wrap, and tie off ends with kitchen twine. Repeat process with remaining dough and filling.
4. Transfer stuffed dough to simmering water, partially cover pot, and cook, turning dough after 20 minutes, until tender, about 45 minutes. Carefully transfer strudel to a kitchen towel and remove cheesecloth. Put strudel on a cutting board, trim off 1" from ends, then cut strudel crosswise into 1"-thick slices. Arrange 3 slices, cut side up, on each of 6 plates and dust each with cocoa and confectioners' sugar.