In the bowl of a stand mixer, combine 1 1/2 cups of the all-purpose flour, the wheat flour, salt, yeast, oats and flax. Stir well.
In a 2 cup microwave-safe glass measure or in a saucepan, heat the water and milk together until very hot (about 130 degrees). Add the butter and stir until it is soft (it doesn't have to be completely melted), then pour water mixture and honey (or maple syrup) into the bowl with the flour. Stir by hand to make a soft dough, and add just enough of the remaining half cup of flour to make a dough that is neither too sticky nor too dry.
Set the bowl on a stand mixer, attach the dough hook and knead for about 8 minutes.
Put the dough in a greased bowl, then cover and let rise for an hour. Punch down dough and fit into a greased 8 1/2 by 4 1/2 inch or 9x5 inch loaf pan. Cover loosely and let rise for another 45 minutes or so.
Preheat the oven to 375 degrees F. If desired, brush top of loaf with egg white and sprinkle with more oats. I did not use egg whites and the oats kept falling off!
Bake for 30 to 35 minutes or until loaf sounds hollow. Let the loaf cool completely (at least 2 hours).