In a large bowl combine whole wheat flour, dry milk powder, the 2 tablespoons sugar, the yeast, and salt. Add the hot water and 1/2 cup of the peanut butter. Beat with an electric mixer on low speed for 30 seconds, scraping bowl constantly. Add 1 cup of the bread flour. Beat on low to medium speed for 30 seconds. Beat on high speed for 3 minutes. Using a wooden spoon, stir in as much of the remaining bread flour as you can.
Turn dough out onto a lightly floured surface. Knead in enough of the remaining bread flour to make a moderately soft dough that is smooth and elastic (3 to 5 minutes total). Shape dough into a ball. Place dough in a lightly greased bowl, turning once to grease surface of the dough. Cover; let rise in a warm place until double in size (about 30 minutes).
Punch down dough. Turn out onto a lightly floured surface. Divide in half. Cover; let rest for 10 minutes. Meanwhile, lightly grease two 9x9x2-inch square baking pans; set aside.
For filling, in a small bowl combine the 1/2 cup sugar and the cinnamon.
Roll each dough half into a 14x6-inch rectangle. Spread each rectangle with 1/4 cup of the remaining peanut butter to within 1/2 inch of the edges. Sprinkle each with sugar-cinnamon mixture. Roll up each rectangle starting from a long side. Seal seams. Slice each roll into nine pieces. Arrange, cut sides down, in prepared pans. Cover and let rise in a warm place until nearly double in size (about 30 minutes).
Preheat oven to 375 degrees F. Bake for 20 to 25 minutes or until browned. Remove from oven. Cool for 1 minute. Carefully invert rolls onto a wire rack. Cool slightly. Invert again onto a serving platter. Spread with Peanut Butter Frosting.
Peanut Butter Frosting
In a medium bowl combine powdered sugar and peanut butter. Stir in enough milk to make a spreading consistency.