- 1/3 cup warm whole milk (105°F to 115°F)
- 1 1/2 teaspoons active dry yeast
- 1 2/3 cups all purpose flour
- 1/2 cup (1 stick) unsalted butter, cut into 1/2-inch cubes, room temperature
Place raisins in small microwave-safe bowl. Cover with water. Microwave on high 1 minute. Let stand until cool.
Stir milk and yeast in large bowl of heavy-duty mixer to blend. Let stand until yeast dissolves, about 8 minutes. Attach dough hook. Add flour and salt to bowl; beat on low speed until blended, scraping sides of bowl often. Whisk eggs and yolk in small bowl to blend. Gradually add eggs to dough, beating on low speed until just blended. Add 3 tablespoons sugar, increase speed to medium, and beat until dough is smooth, scraping sides and bottom of bowl often, about 5 minutes. Reduce speed to medium-low. Add butter, 1 cube at a time, beating to incorporate each (dough will be very soft). Scrape dough off sides of bowl and dough hook. Beat dough until well-blended and pulling away from sides of bowl, about 8 minutes.
Remove bowl from mixer. Drain raisins. Stir raisins into dough. Scrape dough into medium bowl. Cover with plastic wrap and let rise in warm area until doubled in volume, about 1 hour 30 minutes. Using rubber spatula, turn dough over several times in bowl to deflate. Cover again and chill 2 hours, turning to deflate if dough rises. Cover tightly and keep refrigerated overnight.
Generously butter 8- to 9-cup kouglof mold. Roll chilled dough between palms and work surface to 12- to 15-inch rope and place around center post in prepared mold. Cover mold with plastic wrap and let dough rise until almost level with top edge, about 3 hours.
Position rack in center of oven and preheat to 375°F. Bake kouglof uncovered until golden brown on top and tester inserted near center comes out clean, about 20 minutes. Cool in pan 2 minutes. Turn out onto rack and cool.
Sift powdered sugar over kouglof. Cut into wedges and serve.