Sift together flours. Measure 2 cups into large mixer bowl. Add dry yeast, sugar, salt, baking powder, and dry milk. Mix thoroughly.
Combine instant mashed potatoes and hot tap water; whip lightly with a fork.
Add potato mixture and soft butter to dry ingredients in mixer bowl. Beat 3 minutes on medium speed.
Add remaining flour and eggs; beat 3 minutes on medium speed. Mixture will be like thick cake batter.
Leave batter in bowl; cover and let rise in warm place for 1 hour. Batter will rise about 2" depending on size of bowl.
Beat just enough to remove large gas bubbles.
Preheat oven to 325 F.
Grease two 9 x 5 loaf pans. Pour batter into pans; cover and let rise 30 minutes.
Bake 30 to 35 minutes until lightly browned. Especially good toasted.