2 packages (¼ ounce each) active dry yeast
½ cup warm milk (110° to 115°)
¼ cup plus 2 tablespoons sugar
¾ teaspoon salt
1 cup butter, softened
1 cup sour cream
3 large eggs, room temperature, lightly beaten
6 to 6½ cups all-purpose flour
1¼ cups sugar
½ cup butter, cubed
1 large egg
½ teaspoon ground cinnamon
4½ cups ground walnuts
1 large apple, peeled and grated
In a large bowl, dissolve yeast in warm milk. Add the sugar, salt, butter, sour cream, eggs and 3 cups flour. Beat on medium speed for until smooth, 3 minutes. Stir in enough remaining flour to form a soft dough (dough will be sticky).
Turn onto a floured surface; knead until smooth and elastic, 6-8 minutes. Place in a greased bowl, turning once to grease top. Cover and let rise in a warm place until doubled, about 1 hour.
Meanwhile, in a large saucepan, combine the sugar, butter, egg and cinnamon. Cook and stir over medium heat until mixture is thick enough to coat the back of a spoon. Remove from the heat; gently stir in walnuts and apple. Cool completely.
Punch dough down. Turn onto a lightly floured surface; divide into 4 portions. Roll each into a 12x10-in. rectangle. Spread filling to within 1/2 in. of edges. Roll up jelly-roll style, starting with a long side; pinch seams to seal. Place seam side down on greased baking sheets. Cover and let rise until doubled, about 30 minutes.
Bake at 350° for 30-40 minutes or until lightly browned. Remove from pans to wire racks to cool. Combine icing ingredients; drizzle over loaves.