In a large bowl, dissolve yeast in water. Add the milk, honey, shortening, salt, egg, sesame seeds, whole wheat flour and 1-1/2 cups all-purpose flour. Beat until smooth. Stir in enough remaining all-purpose flour to form a stiff dough.
Turn onto a floured surface and knead until smooth and elastic, about 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.
Punch dough down. Turn onto a lightly floured surface; divide in half. Shape into loaves. Place in two greased 9x5-in. loaf pans. Brush with butter; sprinkle with sesame seeds if desired. Cover and let rise until doubled, about 45 minutes.
Bake at 350° for 35-40 minutes or until golden brown. Remove from pans to wire racks to cool.