In large mixing bowl, combine 3 1/2 cups all purpose flour and yeast. In saucepan, heat water, brown sugar, shortening and salt just until warm, stirring constantly to melt shortening. Add to dry mixture in mixing bowl. Beat at low speed with electric mixer for 1/2 minute, scraping sides of bowl constantly. Beat at high speed for three minutes.
By hand, stir in whole wheat flour and enough remaining all purpose flour to make a moderately stiff dough. Turn out onto a lightly floured surface and knead until smoothly and elastic (10 to 12 minutes). Shape into a ball and place dough in a lightly greased bowl, turning once to grease whole surface. Cover and let rise in a warm lace until double (about 1 hour).
Punch dough down; turn out onto light floured surface, divide in half. Cover and let rest 10 minutes. Shape into two loaves and place in two greased loaf pans. Cover and let rise in a warm place until almost double (about 45 minutes). Bake at 375 for 40 to 45 minutes. If necessary, cover loosely with foil the last 20 minutes of baking to prevent over browning. Remove from pans on wire racks, butter tops and cool. Store in plastic bags for not more than 2 days.
