Combine all-purpose flour and yeast in a large mixing bowl, place this to one side. Heat and stir water, butter and brown sugar in a medium saucepan until warm. Add this to the flour and yeast mixture. Use an electric mixer with a dough hook attachment and beat on low to medium speed for 30 seconds, and high speed for 3 minutes. Using a wooden spoon, stir in whole wheat flour.
Place it on a lightly floured surface. Fold the dough and push it downward with the heels of your hands, curving your fingers over the dough. Repeatedly turn the dough, fold it and push it down again for approximately seven minutes. Shape the dough into a ball and place it in a greased bowl. Turn it once, cover it and put it in a warm place, allowing it to rise until double. This step may require 1 1/2 hours.
Next, punch the dough down by making a fist and pushing it into the center of the dough. Press downward through the surface pulling the edges of the dough to the center. Then turn the dough over again and place it in a lightly floured surface. The punched dough should then be divided in half, covered and allowed to sit for 10 minutes. Shape each half of the dough into a loaf and then place it in a lightly greased 8-by-4-by-2 loaf pan. Cover the dough and let it rise until it has nearly doubled in size.
Place the bread in the oven at 375 degrees for 45 minutes or until done. Remove from pans and cool on a wire rack.
Allow the bread to cool at least an hour before slicing. If warm bread is desired, wrap cooled, sliced bread in foil and reheat in oven for 15-20 minutes at 350 degrees.