Dough: Bring milk almost to a boil in a saucepan. Remove from heat, and stir in butter, granulated sugar, vanilla, and salt. Transfer to a large bowl, and let cool until lukewarm, 3 to 5 minutes. Add 1 1/2 cups flour and the yeast, and beat with a mixer on low speed. Beat in eggs and egg yolk, 1 at a time. Beat in remaining 3 cups flour, 1/2 cup at a time. Transfer dough (it will be sticky) to a lightly floured surface, and knead until smooth, about 5 minutes. Place in a buttered bowl, and turn to coat. Cover with plastic wrap, and let rise in a warm place until doubled, about 1 hour. Punch down dough, knead a few times, and let rest 10 minutes. Roll out into a 14-by-22-inch rectangle on a lightly floured surface.
Filling: Mix together brown sugar, raisins, and chocolate. Brush butter on dough, and sprinkle filling on top, leaving a 1-inch border.
Starting from a long side, roll up dough; cut crosswise into 12 slices. Place 6 slices flush against the side of a buttered 10-inch tube pan. Place remaining 6 slices, cut sides together, around tube of pan. Cover, and let rise until doubled, about 1 hour 30 minutes.
Preheat oven to 350 degrees. Bake cake until golden and a toothpick inserted into the center of cake comes out clean, about 40 minutes. Let cool in pan on a wire rack 15 minutes. Unmold, and let cool completely on rack, about 1 hour. Dust with confectioners' sugar before serving.
Gild the Lily
The only thing better than a slice of chocolate kugelhopf is one that's been toasted and spread with sweet butter.