Combine 1 cup all-purpose flour, whole wheat flour, undissolved yeast, and salt in a large mixer bowl. Heat milk, water, honey, and butter until very warm (120° to 130°F). Add to flour mixture. Beat 2 minutes at medium speed of electric mixer, scraping bowl occasionally. Add egg, flax seed, and 1/2 cup flour; beat 2 minutes at high speed. Stir in enough remaining flour to make a soft dough. Knead on lightly floured surface until smooth and elastic, about 8 to 10 minutes. Cover; let rest 10 minutes.
Roll dough to 12 x 8-inch rectangle. Beginning on short end, roll up tightly. Pinch seam and ends to seal. Place, seam side down, in greased 8 -1/2 x 4-1/2 -inch loaf pan. Cover; let rise in warm, draft-free place until doubled in size, about 1-1/2 hours.
Bake at 350°F for 30 to 35 minutes or until done. Remove from pan; cool on wire rack.